Drive control method, drive control device, belt apparatus, image forming apparatus, image reading apparatus, computer product

ABSTRACT

Driving of a pulse motor is controlled in such a manner that a rotating body driven by the pulse motor rotates at a uniform angular velocity. Angular displacement of the rotating body is detected, a difference between a detection value of the angular displacement and a target value of angular displacement set in advance is calculated, and a drive pulse frequency of a drive pulse signal to be used for driving the pulse motor is calculated based on the difference and a reference drive pulse frequency. Whether the difference is added to the reference drive pulse can be selected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 10/937,447, filed Sep. 10, 2004,the entire contents of which is herein incorporated by reference, andclaims the benefit of priority under 35 U.S.C. §119 from Japanesepriority documents, 2003-319038 filed in Japan on Sep. 10, 2003,2003-326822 filed in Japan on Sep. 18, 2003, 2003-328598 filed in Japanon Sep. 19, 2003, 2003-376433 filed in Japan on Nov. 6, 2003, and2004-182596 filed in Japan on Jun. 21, 2004, the entire contents of eachof which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to a drive control method and a drivecontrol device that use a pulse motor, a belt apparatus, an imageforming apparatus, an image reading apparatus, and a computer product.

2) Description of the Related Art

Conventionally, to perform position control of a rotating body, anencoder is arranged on an axis of the rotating body and the rotatingbody is controlled based on feedback from the encoder. The rotating bodymay a cylindrical drum, a circular plate, or a belt laid over at leasttwo shafts. The position control here means angular displacement controlor displacement control.

However, in the conventional technology, eccentricity of the shaft towhich the encoder is attached, eccentricity of an attachment position ofthe encoder with respect to the shaft, and the like causes wrongposition control. One approach to overcome this problem is to fix ascale directly on the surface of the rotating body and read the scalewith a reflective photo-sensor (hereinafter, “sensor”).

However, the scale may become damaged during operation and may produceincorrect readings which leads to incorrect position control.

Moreover, there is always a distinct boundary (hereinafter, “joint”)between the rotating body and the scale, which also produces incorrectreadings. Japanese Patent Application Laid-Open No. 2002-136164discloses a countermeasure. According to this publication, when a pulsedoes not reach within a pre-set time, it is judged that it is a jointthat has produced the incorrect readings. Moreover, rotation velocity ofthe rotating body is corrected based on the judgment.

Japanese Patent Application Laid-Open No. H9-229957 discloses providingreference marks on a rotating drive shaft of the rotating body anddetecting those reference marks. Velocity control and position controlof the rotating body is performed based on result of detection of thereference marks. However, eccentricity of the drive shaft, errors in thepositions of the reference marks, and the like produces incorrectdetection and results in inaccurate feedback control. As acountermeasure, there is known a method of providing reference marksdirectly on the surface of the rotating body.

Most of the existing driving control apparatuses that employ pulsemotors use a feedback control loop for angular displacement, which makesaccurate control of the pulse motor possible. However, this drive systemhas a drawback in that, for example, when a detector breaks down or, inparticular, when there is a wrong output in a detection signal in, forexample, a joint part of a scale at the time when a surface displacementsensor is used, accurate control cannot be performed.

As a countermeasure, Japanese Patent Application Laid-Open No.2002-136164 discloses providing means for interrupting rotating velocitycorrection in a velocity control apparatus of the rotating body in whicha feedback system using a pulse motor is established. However, with onlya velocity control system, it is impossible to cope with a highlyaccurate position control system.

In the method described in Japanese Patent Application Laid-Open No.2002-136164 a timer is required for judging the joint. This causes anincrease in cost due to an increase in the number of components.

In treatment of the joint, there is also a method of using pluralsensors and, when one sensor is judged as abnormal, switching the sensorto another sensor. However, two or more sensors are required in thismethod, and an increase in cost is also unavoidable.

In addition, the method described in Japanese Patent ApplicationLaid-Open No. 2002-136164 is based on an idea of providing two sensorspreliminarily assuming that accuracy is not guaranteed by detection withone sensor. Thus, an increase in cost by an increase in the number ofsensors is unavoidable. In addition, when abnormality has occurs withtime in an optical pattern (scale) that is a detection object, thenumber of sensors is meaningless, and suspension and the like of anapparatus operation are unavoidable.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve at least the problemsin the conventional technology.

A drive control method according to an aspect of the present inventionis a method of controlling driving of a pulse motor such that a rotatingbody driven by the pulse motor rotates at uniform angular velocity. Thedrive control method includes detecting angular displacement of therotating body; calculating a difference between a detection value of theangular displacement and a target value of angular displacement set inadvance; and calculating a drive pulse frequency of a drive pulse signalto be used for driving for the pulse motor based on the difference and areference drive pulse frequency to make it possible to select whetherthe difference is added to the reference drive pulse.

A drive control method according to another aspect of the presentinvention is a method of controlling driving of a pulse motor such thata moving body driven by the pulse motor moves at a uniform velocity. Thedrive control method includes detecting displacement of the moving body;calculating a difference between a detection value of the displacementand a target value of displacement set in advance; calculating a drivepulse frequency of a drive pulse signal to be used for driving for thepulse motor based on the difference and a reference drive pulsefrequency, and selecting whether the difference is added to thereference drive pulse.

A drive control device according to still another aspect of the presentinvention is a device that controls driving of a pulse motor such that arotating body driven by the pulse motor rotates at uniform angularvelocity. The drive control device includes an angular displacementdetecting unit that detects angular displacement of the rotating body; adifference calculating unit that calculates a difference between adetection value of the angular displacement and a target value ofangular displacement set in advance; and a drive pulse frequencycalculating unit that calculates a drive pulse frequency of a drivepulse signal to be used for driving for the pulse motor based on thedifference and a reference drive pulse frequency to make it possible toselect whether the difference is added to the reference drive pulse.

A drive control device according to still another aspect of the presentinvention is a device that controls driving of a pulse motor such that amoving body driven by the pulse motor moves at a uniform velocity. Thedrive control device includes a difference calculating unit thatcalculates a difference between a detection value of displacement of themoving body and a target value of displacement set in advance; a drivepulse frequency calculating unit that calculates a drive pulse frequencyof a drive pulse signal to be used for driving for the pulse motor basedon the difference and a reference drive pulse frequency; and a selectingunit that makes it possible to select whether the difference is added tothe reference drive pulse.

A belt apparatus according to still another aspect of the presentinvention includes a belt that is laid over plural support rotatingbodies; the above drive control device that controls driving of thebelt; and a drive device that drives the belt based on a drive pulsefrequency output from the drive control device.

An image forming apparatus according to still another aspect of thepresent invention includes an image bearing member; the above drivecontrol device that controls driving of the image bearing member; and adrive device that drives the image bearing member based on a drive pulsefrequency output from the drive control device.

An image forming apparatus according to still another aspect of thepresent invention includes a plurality of image bearing members; theabove drive control device that controls driving of the image bearingmembers; and a drive device that drives the image bearing members basedon a drive pulse frequency output from the drive control device.

An image reading apparatus according to still another aspect of thepresent invention includes a moving body that includes an optical systemfor image reading; the above drive control device that controls drivingfor the moving body; and a drive device that drives the moving bodybased on a drive pulse frequency output from the drive control device.

A position control method according to still another aspect of thepresent invention is a method of feedback-controlling displacement in arotating direction of a rotating body, which is driven to rotate by adrive source, by reading a signal generated according to rotation of therotating body. When a signal amount read in sampling time is outside arange compared with a defined signal amount, correction processing for afeedback signal is performed.

A position control method according to still another aspect of thepresent invention is a method of feedback-controlling displacement in arotating direction of a rotating body, which is driven to rotate by adrive source, by reading a scale pulse generated based on a scaleprovided in the rotating body. When a scale pulse number read insampling time is outside a range compared with a defined scale pulsenumber, correction processing for a feedback signal is performed.

A position control device according to still another aspect of thepresent invention controls position of a rotating body. The positioncontrol device includes a signal generating unit that is provided in arotating body driven to rotate by a drive source, which operates inresponse to a control signal, and generates a signal for detectingdisplacement in a rotating direction of the rotating body; and a controlunit that reads the signal generated by the signal generating unit,feedbacks the signal, calculates a deviation between presentdisplacement and a target displacement, and outputs the control signalanew. When a signal amount read in sampling time is outside a rangecompared with a defined signal amount, the control unit performscorrection processing for a feedback signal.

A position control device according to still another aspect of thepresent invention controls position of a rotating body. The positioncontrol device includes a scale that is provided in a rotating bodydriven to rotate by a drive source, which operates in response to acontrol signal; a scale pulse generating unit that generates a pulse fordetecting displacement in a rotating direction of the rotating bodybased on the scale; and a control unit that reads a scale pulsegenerated by the scale pulse generating unit, feedbacks the scale pulse,calculates a deviation between present displacement and targetdisplacement, and outputs the control signal anew. When a scale pulsenumber read in sampling time is outside a range compared with a definedscale pulse number, the control unit performs correction processing fora feedback signal.

An image forming apparatus according to still another aspect of thepresent invention includes an image bearing member on which an image isformed; and the above position control device that drive controls theimage bearing member.

An image forming apparatus according to still another aspect of thepresent invention includes a plurality of image bearing members on whicha color image is formed; and the above position control device thatdrive controls at least one of the image bearing members.

An image reading apparatus according to still another aspect of thepresent invention includes a traveling body drive device that reads animage; and the above position control device that drive controls thetraveling body drive device.

A position control method according to still another aspect of thepresent invention is a method of controlling displacement in a rotatingdirection of a rotating body, which is driven to rotate by a drivesource, by reading signals generated according to rotation of therotating body. The signals are two kinds of signals, namely, a firstsignal generated by rotation of the rotating body itself and a secondsignal generated by rotation of a shaft of the rotating body, and thesetwo signals are used as a control signal selectively.

A position control device according to still another aspect of thepresent invention controls position of a rotating body. The positioncontrol device includes a first signal generating unit that is providedin a rotating body driven to rotate by a drive source and generates afirst signal for detecting displacement in a rotating direction of therotating body; a second signal generating unit that is provided in ashaft of the rotating body and generates a second signal for detectingdisplacement in a rotating direction of the shaft; and a control unitthat controls the drive source based on the signal generated by thefirst signal generating unit or the second signal generating unit. Thecontrol unit uses the two signals as a control signal selectively.

An image forming apparatus according to still another aspect of thepresent invention includes an image bearing member on which an image isformed; and the above position control device that drive controls theimage bearing member.

An image forming apparatus according to still another aspect of thepresent invention includes a plurality of image bearing members on whichan image is formed respectively; and the above position control devicethat drive controls at least one of the image bearing members.

An image reading apparatus according to still another aspect of thepresent invention includes a traveling body drive device that reads animage; and the above position control device that drive controls thetraveling body drive device.

A drive control device according to still another aspect of the presentinvention includes a mark detecting unit that detects plural marks thatare provided on a drive control object member at predetermined intervalalong a direction of movement of the drive control object member, orthat detects plural marks that are provided on an endless moving memberat predetermined interval along a direction of movement of the endlessmoving member, wherein the drive control object member and the endlessmoving member move endlessly, wherein the mark detecting unit outputs amark detection signal when a mark is detected; a multiplying unit thatgenerates a multiplied signal by increasing by a predetermined times amagnitude of the mark detection signal; and a feedback control unit thatperforms feedback control using the multiplied signal when it is judgedthat a discontinuous part, where intervals of signal parts correspondingto the marks are outside a range decided in advance, is not present inthe mark detection signal or the multiplied signal and performs thefeedback control using an alternative signal instead of the multipliedsignal when it is judged that the discontinuous part is present.

A drive control method according to still another aspect of the presentinvention includes detecting plural marks that are provided on a drivecontrol object member at predetermined interval along a direction ofmovement of the drive control object member, or that detects pluralmarks that are provided on an endless moving member at predeterminedinterval along a direction of movement of the endless moving member,wherein the drive control object member and the endless moving membermove endlessly; outputting a mark detection signal when a mark isdetected and the mark detection signal; generating a multiplied signalby increasing by a predetermined times a magnitude of the mark detectionsignal; and performing feedback control using the multiplied signal whenit is judged that a discontinuous part, where intervals of signal partscorresponding to the marks are outside a range decided in advance, isnot present in the mark detection signal or the multiplied signal andperforms the feedback control using an alternative signal instead of themultiplied signal when it is judged that the discontinuous part ispresent.

An image forming apparatus according to still another aspect of thepresent invention includes a drive control object member that movesendlessly; and the above drive control device that drive controls thedrive control object member.

A drive control device according to still another aspect of the presentinvention includes a mark detecting unit that detects plural marks thatare provided on a drive control object member at predetermined intervalalong a direction of movement of the drive control object member, orthat detects plural marks that are provided on an endless moving memberat predetermined interval along a direction of movement of the endlessmoving member, wherein the drive control object member and the endlessmoving member move endlessly, wherein the mark detecting unit outputs amark detection signal when a mark is detected; a feedback control unitthat performs feedback control using an alternative signal instead ofthe mark detection signal at least for one of a discontinuous part inthe mark detection signal where intervals of signal parts correspondingto the respective marks are outside a range decided in advance andsignal parts immediately before and after the discontinuous part.

A drive control method according to still another aspect of the presentinvention includes detecting plural marks that are provided on a drivecontrol object member at predetermined interval along a direction ofmovement of the drive control object member, or that detects pluralmarks that are provided on an endless moving member at predeterminedinterval along a direction of movement of the endless moving member,wherein the drive control object member and the endless moving membermove endlessly; outputting a mark detection signal when a mark isdetected and the mark detection signal; and performing feedback controlusing an alternative signal instead of the mark detection signal atleast for one of a discontinuous part in the mark detection signal whereintervals of signal parts corresponding to the respective marks areoutside a range decided in advance and signal parts immediately beforeand after the discontinuous part.

An image forming apparatus according to still another aspect of thepresent invention includes a drive control object member that movesendlessly; and the above drive control device that drive controls thedrive control object member.

An image reading apparatus according to still another aspect of thepresent invention includes a traveling body that irradiates light on anoriginal surface or receives reflected light of light irradiated on theoriginal surfaced; a drive control object member, which moves endlessly,provided on a drive force transmission path for transmitting a driveforce for causing the traveling member to travel along the originalsurface; and the above drive control device that drive controls thedrive control object member.

A computer program according to still another aspect of the presentinvention realizes the above drive control method on a computer. Acomputer-readable recording medium according to still another aspect ofthe present invention stores therein the above computer program.

The other objects, features, and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of the invention when read in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an appearance of a pulse motor accordingto a first embodiment of the invention;

FIG. 2 is a block diagram of a structure of a digital control systemaccording to the first embodiment;

FIG. 3 is a block diagram of drive control for a rotating body accordingto the first embodiment;

FIG. 4 is a perspective view of an appearance of a pulse motor accordingto a second embodiment of the invention;

FIG. 5 is a block diagram of a structure of a digital control systemaccording to the second embodiment;

FIG. 6 is a block diagram of a structure of the digital control systemaccording to the second embodiment;

FIG. 7 is a perspective view of an appearance of a pulse motor accordingto a third embodiment of the invention;

FIG. 8 is a diagram of a structure of a digital control system accordingto the third embodiment;

FIG. 9 is a block diagram of a drive system for a rotating bodyaccording to the third embodiment;

FIG. 10 is a perspective view of an appearance of a pulse motoraccording to a fourth embodiment of the invention;

FIG. 11 is a block diagram of a structure of a digital control systemaccording to the fourth embodiment;

FIG. 12 is a block diagram of drive control for a rotating bodyaccording to the fourth embodiment;

FIG. 13 is a block diagram of drive control for a rotating bodyaccording to a fifth embodiment of the invention;

FIG. 14 is a perspective view of a belt drive apparatus according to aseventh embodiment of the invention;

FIG. 15 is a perspective view of a rotating body (drum) drive apparatus;

FIGS. 16A and 16B are plan views of a joint of a linear scale;

FIG. 17 is a block diagram of a current control system;

FIG. 18 is a block diagram of a current control system in anotherexample;

FIG. 19 is a conceptual diagram for grasping a pulse count number persampling time;

FIG. 20 is a block diagram of a feedback control system in aconventional technique;

FIG. 21 is a block diagram of a feedback control system according to theseventh embodiment;

FIG. 22 is a graph of a relation between time and a pulse count numberper a sampling time for explaining a position control method for arotating body according to the seventh embodiment;

FIG. 23 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to an eighth embodiment of the invention;

FIG. 24 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a ninth embodiment of the invention;

FIG. 25 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a tenth embodiment of the invention;

FIG. 26 is a graph of a basic concept of a relation between time and apulse count number per sampling time according to an eleventh embodimentof the invention;

FIG. 27 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to the eleventh embodiment;

FIG. 28 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a twelfth embodiment;

FIG. 29 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a thirteenth embodiment;

FIG. 30 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a fourteenth embodiment;

FIG. 31 is a graph of a basic concept of a relation between time and apulse count number per sampling time according to a fifteenth embodimentof the invention;

FIG. 32 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to the fifteenth embodiment;

FIG. 33 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a sixteenth embodiment;

FIG. 34 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to a seventeenth embodiment;

FIG. 35 is a graph of a relation between time and a pulse count numberper sampling time for explaining a position control method for arotating body according to an eighteenth embodiment of the invention;

FIG. 36 is a flowchart of error detection, error processing, and anoperation of a control system at the time when a counter has a resetfunction;

FIG. 37 is a flowchart of error detection, error processing, and anoperation of a control system at the time when a counter does not have areset function;

FIG. 38 is a perspective view of a belt drive apparatus according to anineteenth embodiment of the invention;

FIG. 39 is a perspective view of a rotating body (drum) drive apparatus:

FIG. 40 is a main part plan view of a writing pattern of a linear scale;

FIG. 41 is a block diagram of a current control system;

FIG. 42 is a block diagram of a feedback control system in aconventional technique;

FIG. 43 is a block diagram of a feedback control system according to thenineteenth embodiment;

FIG. 44 is a flowchart of selection control for a signal in a positioncontrol method for a rotating body according to the nineteenthembodiment;

FIG. 45 is a flowchart of selection control for a signal according to atwentieth embodiment of the invention;

FIG. 46 is a flowchart of selection control for a signal according to atwenty-first embodiment of the invention;

FIG. 47 is a flowchart of selection control for a signal according to atwenty-second embodiment of the invention;

FIG. 48 is a flowchart of selection control for a signal according to atwenty-third embodiment of the invention;

FIG. 49 is a flowchart of selection control for a signal according to atwenty-fourth embodiment of the invention;

FIG. 50 is a flowchart of selection control for a signal according to atwenty-fifth embodiment of the invention;

FIG. 51 is a flowchart of selection control for a signal according to atwenty-sixth embodiment of the invention;

FIG. 52 is a flowchart of selection control for a signal according to atwenty-seventh embodiment of the invention;

FIG. 53 is a flowchart of selection control for a signal according to atwenty-eighth embodiment of the invention;

FIG. 54 is a flowchart of selection control for a signal according to atwenty-ninth embodiment of the invention;

FIG. 55 is a flowchart of selection control for a signal according to athirtieth embodiment of the invention;

FIGS. 56A and 56B are plan views of a joint of a linear scale;

FIG. 57 is a flowchart of selection control for a signal according to athirty-first embodiment of the invention;

FIG. 58 is a flowchart of selection control for a signal according to athirty-second embodiment of the invention;

FIG. 59 is a flowchart of selection control for a signal according to athirty-third embodiment of the invention;

FIG. 60 is a diagram of a structure of a first signal generating unit;

FIG. 61 is a graph of a state of output by a surface sensor;

FIG. 62 is a diagram showing an output by the surface sensor as arectangular pulse;

FIG. 63 is a diagram of criteria for judgment of abnormality in anoutput signal output by the surface sensor;

FIG. 64 is a graph of a relation between time and a pulse count numberper sampling time in the diagram of criteria for judgment of abnormalityin an output signal output by the surface sensor;

FIG. 65 is a graph for explaining positions of a belt and a drum withrespect to a target position before and after a period of adiscontinuous part in a feedback control system that does not multiply asensor output;

FIG. 66 is a schematic diagram of a structure of belt drive apparatusthat is an embodiment of the invention;

FIG. 67 is a schematic diagram of a structure of a drum drive apparatusthat is another embodiment of the invention;

FIGS. 68A and 68B are enlarged views of a joint part of a linear scale;

FIG. 69 is a block diagram of a structure of a control system thatsubjects angular displacement of a motor to digital control based on anoutput signal of a surface sensor;

FIG. 70 is a control block diagram of a schematic structure of afeedback control system according to an embodiment of the invention;

FIG. 71 is a functional block diagram of a multiplying circuit thatconstitutes a multiplying unit constituting the feedback control system;

FIG. 72 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part at the time when correctionprocessing by a correction processing unit is not performed;

FIG. 73 is a flowchart of a flow of control in the feedback controlsystem;

FIG. 74 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part at the time when correctionprocessing by the correction processing unit is performed;

FIG. 75A is a diagram of an output pulse before multiplication and amultiplied pulse after the multiplication;

FIG. 75B is a diagram of an output pulse before multiplication and amultiplied pulse after the multiplication;

FIG. 76 is a graph for explaining positions of a belt and a drum withrespect to a target position before and after a period of adiscontinuous part at the time when the feedback control system is used;

FIG. 77 is a timing chart for explaining a relation between an outputpulse output from a surface sensor and an operation of a multiplyingunit;

FIG. 78 is a flowchart of a flow of control in a feedback control systemaccording to a modification;

FIG. 79 is a graph of a light receiving level of a surface sensor, acomparative result signal, and a multiplied signal for explaininganother example of a structure according to the modification;

FIG. 80A is an enlarged view of a joint part of a linear scale;

FIG. 80B is a diagram of a light receiving level of a surface sensor fordetecting a linear scale;

FIG. 80C is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 81A is an enlarged view of a joint part of a linear scale in whichend turn-up has occurred;

FIG. 81B is a diagram of a light receiving level of a surface sensor fordetecting the linear scale;

FIG. 81C is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 82A is an enlarged view of a stain part adhering on a linear scale;

FIG. 82B is a diagram of a light receiving level of a surface sensor fordetecting the linear scale;

FIG. 82C is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 83A is a block diagram of a structure of a control system thatsubjects angular displacement of a motor to digital control based on anoutput signal of a surface sensor;

FIG. 83B is a block diagram of a structure of a control system thatsubjects angular displacement of a motor to digital control based on anoutput signal of a surface sensor;

FIG. 84 is a control block diagram of a schematic structure of afeedback control system according to an embodiment of the invention;

FIG. 85A is a diagram of a light receiving level of a surface sensor ina first operation example;

FIG. 85B is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 85C is a diagram of a mark control signal in the first operationexample;

FIG. 86 is a functional block diagram of a multiplying circuit thatconstitutes a multiplying unit constituting the feedback control system;

FIG. 87 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part at the time when correctionprocessing by a correction processing unit is not performed;

FIG. 88 is a flowchart of a flow of control of a feedback control systemin the first operation example;

FIG. 89 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part at the time when correctionprocessing by the correction processing unit is performed;

FIG. 90A is a diagram of an output pulse before multiplication and amultiplied pulse after the multiplication;

FIG. 90B is a diagram of an output pulse before multiplication and amultiplied pulse after the multiplication;

FIG. 91A is a diagram of a light receiving level of a surface sensor ina second operation example;

FIG. 91B is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 91C is a diagram showing a mark control signal in the secondoperation example;

FIG. 92 is a flowchart of a flow of control of a feedback control systemin the second operation example;

FIG. 93A is a diagram of a light receiving level of a surface sensor ina third operation example;

FIG. 93B is a diagram of an output pulse of the surface sensor that isoutput according to the light receiving level;

FIG. 93C is a diagram of a mark control signal in a third operationexample;

FIG. 94A is an explanatory diagram of an example of generation of a maskcontrol signal;

FIG. 94B is an explanatory diagram of an example of generation of a maskcontrol signal;

FIG. 95 is an explanatory diagram for explaining another example of amethod of judging a discontinuous part;

FIG. 96 is a schematic front view of a color copying machine serving asan image forming apparatus according to a thirty-sixth embodiment of theinvention;

FIG. 97 is a schematic front view of a color copying machine serving asan image forming apparatus according to a thirty-seventh embodiment ofthe invention;

FIG. 98 is a schematic front view of a color copying machine serving asan image forming apparatus according to a thirty-eighth embodiment ofthe invention;

FIG. 99 is a schematic front view of an image reading apparatusaccording to a thirty-ninth embodiment of the invention;

FIG. 100 is a schematic front view of a computer in which a CD-ROMserving as a recording medium according to a fortieth embodiment of theinvention is usable;

FIG. 101 is a main part block diagram of a computer in which an IC cardserving as the recording medium is usable;

FIG. 102 is a main part block diagram of an image forming apparatus of asystem for fetching a computer program (hereinafter, “program”) from anetwork according to a forty-first embodiment of the invention; and

FIG. 103 is a main part block diagram of an image forming apparatusincluding a display apparatus according to the forty-first embodiment.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will be explained belowwith reference to the accompanying drawings.

FIG. 1 shows a rotating body, a power transmission system, and a pulsemotor serving as a rotation drive source according to a first embodimentof the invention. The first embodiment is an example of a rotating bodydrive control device. In FIG. 1, reference numeral 1501 denotes a pulsemotor serving as a rotation drive source that drives to rotate arotating body. A rotation torque of the pulse motor 1501 is transmittedto a shaft 1506 of a rotating body 1505 by a train of gears 1503 and atiming belt 1504 that constitute a power transmission system. Therotating body 1505 is fixed to the shaft 1506 firmly. Reference numeral1507 denotes an encoder serving as a state detection device that detectsangular displacement of the rotating body 1505. The encoder 1507 isattached to the shaft 1506 of the rotating body 1505 via a coupling (notshown). It is needless to mention that angular displacement of the shaft1506 to be detected by the encoder 1507 is the same as angulardisplacement of the rotating body 1505.

FIG. 2 shows a structure of a control system that subjects angulardisplacement of the pulse motor 1501 to digital control based on a statedetection signal for the rotating body 1505 (in this context, an outputsignal of the encoder 1507). In FIG. 2, reference numeral 1 denotes amicrocomputer including a microprocessor 2, and a read only memory (ROM)3, a random access memory (RAM) 4. The microprocessor 2, the read onlymemory (ROM) 3, and the random access memory (RAM) 4 are connected toone another via a bus 9.

Reference numeral 5 denotes an instruction generating device thatoutputs a state instruction signal for instructing target angulardisplacement of the rotating body 1505. The instruction generatingdevice 5 generates an angular displacement instruction signal. An outputside of the instruction generating device 5 is also connected to the bus9. Reference numeral 10 denotes an interface device for detection thatprocesses an output pulse of the encoder 1507 and converts the outputpulse into a digital numerical value. The interface device for detection10 includes a counter that counts an output pulse of the encoder 1507.The interface device for detection 10 multiplies a numerical valuecounted by the counter by a predetermined conversion constant of pulsenumber versus angular displacement and converts the numerical value intoangular displacement of the rotating body 1505. Reference numeral 6denotes an interface for pulse motor drive. The interface for pulsemotor drive 6 converts a result of arithmetic operation (control output)of the microcomputer 1 into a pulse-like signal (control signal) foractuating, for example, a power semiconductor constituting a pulse motordrive device 7. The pulse motor drive device 7 operates based on thepulse-like signal from the interface for pulse motor drive 6 and drivesto rotate the pulse motor. As a result, the rotating body 1505 iscontrolled to follow up predetermined angular displacement instructed bythe instruction generating device 5. The angular displacement of therotating body 1505 is detected by the encoder 1507 and the interfacedevice 10 and taken into the microcomputer 1, and these operations arerepeated. Here, reference numeral 11506 denotes a block indicating therotating body 1505, and 11510 denotes a block indicating the gear powertransmission system 1503 and the timing belt power transmission system1504 shown in FIG. 1.

Next, drive control for a rotating body, which controls the rotatingbody 1505 to come into a uniform angular velocity state by controllingrotation angle displacement of the rotating body 1505 with the pulsemotor 1501 according to the embodiment constituted as described above,will be explained with reference to a block structure of the embodimentshown in FIG. 3.

In FIG. 3, reference numeral 801 denotes a control object including theentire rotating body drive system shown in FIG. 1 and the interface forpulse motor drive 6, the pulse motor drive device 7, and the interfacedevice 10 shown in FIG. 2 in the embodiment. An output from theinterface device 10 that processes an output from the encoder 1507, thatis, angular displacement information P301(i−1) of the rotating body 1505is given to an arithmetic operation unit 304. The arithmetic operationunit 304 calculates a difference e(i) between target angulardisplacement Ref(i) of the rotating body 1505, which is a control targetvalue, and angular displacement P301(i−1) of the rotating body 1505. Thearithmetic operation unit 304 inputs the difference e(i) to a controllerunit 305. The controller unit 305 is constituted by, for example, a PIcontrol system. The difference e(i) calculated in the arithmeticoperation unit 304 is integrated in a block 306, multiplied by aconstant KI in a block 307, and given to an arithmetic operation unit308. Simultaneously, the difference e(i) calculated in the arithmeticoperation unit 304 is multiplied by a constant KP in a block 309 andgiven to the arithmetic operation unit 308. The arithmetic operationunit 308 adds two input signals from the blocks 307 and 309 and gives aresult of the addition to a feedback signal selecting unit 311. Thefeedback signal selecting unit 311 receives a feedback judgment signal,selects an output from the arithmetic operation unit 308 or a constant0, and gives the output or the constant 0 to an arithmetic operationunit 310. In short, the feedback signal selecting unit 311 selects theoutput from the arithmetic operation unit 308 when feedback is performedand selects the constant 0 when feedback is not performed. The feedbackjudgment signal can be given as, for example, an arbitrary I/O signalaffected by abnormality of a sensor or the like. It is needless tomention that the feedback signal selecting unit 311 selects the outputfrom the arithmetic operation unit 308 when there is no abnormality andselects the constant 0 when there is abnormality. Thereafter, thearithmetic operation unit 310 adds a constant pulse input Refp_c anddetermines a drive pulse frequency u(i).

The drive pulse frequency u(i) calculated in the arithmetic operationunit 310 is output to the pulse motor 1501 via the interface for pulsemotor drive 6 and the pulse motor drive device 7, the rotating body 1505rotates via a transmission system, and the loop operation describedabove is repeated. Although a PI control system is used as thecontroller unit 305 as an example, the controller unit 305 is notlimited to this. All the above-mentioned arithmetic operations areperformed by a numerical operation in the microcomputer 1 and can berealized easily. Refp_c is a pulse number that is determined uniquelybased on a rotating body angular velocity and a reduction gear ratio ofa deceleration system. However, in the invention, it is also possible toselect a pulse number arbitrarily within a range in which a step-outphenomenon does not occur during motor driving. In addition, Ref(i) canbe calculated easily by integrating a target uniform angular velocity ofthe rotating body 1505.

According to the first embodiment, when there is abnormality, usualpulse motor drive is performed without performing feedback. Thus, aposition control system in a pulse motor drive system, which is capableof carrying out accurate and highly accurate control even when there isa wrong output in a detection signal due to influence of noise or thelike caused by failure and abnormality in a sensor, can be established.

Next, a second embodiment of the invention will be explained. The secondembodiment is an example of a belt conveyance control method to whichthe invention is applied.

In FIG. 4, reference numeral 1501 denotes a pulse motor serving as arotation drive source for driving to rotate a belt 1502. A rotationtorque of the pulse motor 1501 is transmitted to the drive shaft 1506and the drive roller 1505 for the belt by a deceleration system, forexample, a timing belt 1503 constituting a power transmission system.The belt is wound around the drive roller 1505 and driven rollers 1510,1511, 1512, 1513, and 1514. Therefore, when the drive roller 1505 isrotated by the pulse motor 1501, the belt 1502 moves accordingly.

Reference numeral 1507 denotes an encoder serving as a state detectingdevice for detecting angular displacement of the drive roller 1505. Theencoder 1507 is attached to the shaft 1506 of the drive roller 1505 viaa coupling (not shown).

A belt conveying apparatus shown in FIG. 4 is subjected to drive controlin a control system shown in FIGS. 5 and 6.

FIG. 5 shows a structure of a control system that subjects angulardisplacement of the pulse motor 1501 to digital control based on a statedetection signal for the drive roller 1505 (in this context, an outputsignal of the encoder 1507). In FIG. 5, reference numeral 1 denotes amicrocomputer including the microprocessor 2, and the read only memory(ROM) 3, the random access memory (RAM) 4. The microprocessor 2, theread only memory (ROM) 3, and the random access memory (RAM) 4 areconnected to one another via the bus 9.

Reference numeral 5 denotes an instruction generating device thatoutputs a state instruction signal for instructing target angulardisplacement of the drive roller 1505. The instruction generating device5 generates an angular displacement instruction signal. An output sideof the instruction generating device 5 is also connected to the bus 9.Reference numeral 10 denotes an interface device for detection thatprocesses an output pulse of the encoder 1507 and converts the outputpulse into a digital numerical value. The interface device for detection10 includes a counter that counts an output pulse of the encoder 1507.The interface device for detection 10 multiplies a numerical valuecounted by the counter by a predetermined conversion constant of pulsenumber versus angular displacement and converts the numerical value intoangular displacement of the drive roller 1505. Reference numeral 6denotes an interface for pulse motor drive. The interface for pulsemotor drive 6 converts a result of arithmetic operation (control output)of the microcomputer 1 into a pulse-like signal (control signal) foractuating, for example, a power semiconductor constituting a pulse motordrive device 7. The pulse motor drive device 7 operates based on thepulse-like signal from the interface for pulse motor drive 6 and drivesto rotate the pulse motor. As a result, the drive roller 1505 iscontrolled to follow up predetermined angular displacement instructed bythe instruction generating device 5. As a result, the belt 1502 woundaround the drive roller 1505 is driven at uniform velocity. The angulardisplacement of the drive roller 1505 is detected by the encoder 1507and the interface device 10 and taken into the microcomputer 1, andthese operations are repeated. Here, reference numeral 11506 denotes ablock indicating the drive roller 1505, and 11510 denotes a blockindicating the timing belt power transmission system 1503 shown in FIG.4.

Next, drive control for a belt, which controls the belt to come into auniform angular velocity state by controlling rotation angledisplacement of the drive roller 1505 with the pulse motor 1501according to the embodiment constituted as described above, will beexplained with reference to a block structure of the embodiment shown inFIG. 6. In FIG. 6, reference numeral 801 denotes a control objectincluding the entire rotating body drive system shown in FIG. 4 and theinterface for pulse motor drive 6, the pulse motor drive device 7, andthe interface device 10 shown in FIG. 5 in the embodiment.

An output from the interface device 10, which processes an output fromthe encoder 1507, that is, angular displacement information P301(i−1) ofthe rotating body 1505, is given to an arithmetic operation unit 304.The arithmetic operation unit 304 calculates a difference e(i) betweentarget angular displacement Ref(i) of the rotating body 1505, which is acontrol target value, and angular displacement P301(i−1) of the rotatingbody 1505. The arithmetic operation unit 304 inputs the difference e(i)to a controller unit 305.

The controller unit 305 is constituted by, for example, a PI controlsystem. The difference e(i) calculated in the arithmetic operation unit304 is integrated in the block 306, multiplied by a constant KI in theblock 307, and given to the arithmetic operation unit 308. At the sametime, the difference e(i) calculated in the arithmetic operation unit304 is multiplied by a constant KP in the block 309 and given to thearithmetic operation unit 308. The arithmetic operation unit 308 addstwo input signals from the blocks 307 and 309 and gives a result of theaddition to the feedback signal selecting unit 311. The feedback signalselecting unit 311 receives a feedback judgment signal, selects anoutput from the arithmetic operation unit 308 or a constant 0, and givesthe output or the constant 0 to the arithmetic operation unit 310. Inshort, the feedback signal selecting unit 311 selects the output fromthe arithmetic operation unit 308 when feedback is performed and selectsthe constant 0 when feedback is not performed. The feedback judgmentsignal can be given as, for example, an arbitrary I/O signal affected byabnormality of a sensor or the like. It is needless to mention that thefeedback signal selecting unit 311 selects the output from thearithmetic operation unit 308 when there is no abnormality and selectsthe constant 0 when there is abnormality. Thereafter, the arithmeticoperation unit 310 adds a constant pulse input Refp_c and determines adrive pulse frequency u(i).

The drive pulse frequency u(i) calculated in the arithmetic operationunit 310 is output to the pulse motor 1501 via the interface for pulsemotor drive 6 and the pulse motor drive device 7, the rotating body 1505rotates via a transmission system, and the loop operation describedabove is repeated. Although a PI control system is used as thecontroller unit 305 as an example, the controller unit 305 is notlimited to this. All the above-mentioned arithmetic operations areperformed by a numerical operation in the microcomputer 1 and can berealized easily.

Refp_c is a pulse number that is determined uniquely based on a rotatingbody angular velocity and a reduction gear ratio of a decelerationsystem. However, in the invention, it is also possible to select a pulsenumber arbitrarily within a range in which a step-out phenomenon doesnot occur during motor driving. In addition, Ref(i) can be calculatedeasily by integrating a target uniform angular velocity of the rotatingbody 1505.

According to the second embodiment, when there is abnormality, usualpulse motor drive is performed without performing feedback. Thus, a beltposition control system in a pulse motor drive system, which is capableof carrying out accurate and highly accurate control even when there isa wrong output in a detection signal due to influence of noise or thelike caused by failure and abnormality in a sensor, can be established.

Next, a third embodiment of the invention will be explained. The thirdembodiment is an example of the belt conveyance control method.

In FIG. 7, reference numeral 1501 denotes a pulse motor serving as arotation drive source for driving to rotate the belt 1502. A rotationtorque of the pulse motor 1501 is transmitted to the drive shaft 1506and the drive roller 1505 for the belt by a deceleration system, forexample, the timing belt 1503 constituting the power transmissionsystem. The belt is wound around the drive roller 1505 and the drivenrollers 1510, 1511, 1512, 1513, and 1514. Therefore, when the driveroller 1505 is rotated by the pulse motor 1501, the belt 1502 movesaccordingly.

Reference numeral 1507 denotes an encoder serving as a state detectingdevice for detecting angular displacement of the driven roller 1510. Theencoder 1507 is attached to a shaft of the driven roller 1510 via acoupling 1516.

A belt conveying apparatus shown in FIG. 7 is subjected to drive controlin a control system shown in FIGS. 8 and 9.

FIG. 8 shows a structure of a control system that subjects angulardisplacement of the pulse motor 1501 to digital control based on a statedetection signal for the driven roller 1510 (in this context, an outputsignal of the encoder 1507). In FIG. 8, reference numeral 1 denotes amicrocomputer including the microprocessor 2, the read only memory (ROM)3, and the random access memory (RAM) 4. The microprocessor 2, the readonly memory (ROM) 3, and the random access memory (RAM) 4 are connectedto one another via the bus 9.

Reference numeral 5 denotes an instruction generating device thatoutputs a state instruction signal for instructing target angulardisplacement of the driven roller 1510. The instruction generatingdevice 5 generates an angular displacement instruction signal. An outputside of the instruction generating device 5 is also connected to the bus9. Reference numeral 10 denotes an interface device for detection thatprocesses an output pulse of the encoder 1507 and converts the outputpulse into a digital numerical value. The interface device for detection10 includes a counter that counts an output pulse of the encoder 1507.The interface device for detection 10 multiplies a numerical valuecounted by the counter by a predetermined conversion constant of pulsenumber versus angular displacement and converts the numerical value intoangular displacement of the driven roller 1510. Reference numeral 6denotes an interface for pulse motor drive. The interface for pulsemotor drive 6 converts a result of arithmetic operation (control output)of the microcomputer 1 into a pulse-like signal (control signal) foractuating, for example, a power semiconductor constituting a pulse motordrive device 7. The pulse motor drive device 7 operates based on thepulse-like signal from the interface for pulse motor drive 6 and drivesto rotate the pulse motor. As a result, the driven roller 1510 iscontrolled to follow up predetermined angular displacement instructed bythe instruction generating device 5. As a result, the belt 1502 woundaround the driven roller 1510 is driven at uniform velocity. The angulardisplacement of the driven roller 1510 is detected by the encoder 1507and the interface device 10 and taken into the microcomputer 1, andthese operations are repeated. Here, reference numeral 11506 denotes ablock indicating the belt conveying apparatus, and 11510 denotes a blockindicating the timing belt power transmission system 1503 shown in FIG.7.

Next, drive control for a belt, which controls the belt to come into auniform angular velocity state by controlling rotation angledisplacement of the driven roller 1510 with the pulse motor 1501according to the embodiment constituted as described above, will beexplained with reference to a block structure of the embodiment shown inFIG. 9. In FIG. 9, reference numeral 801 denotes a control objectincluding the entire rotating body drive system shown in FIG. 7 and theinterface for pulse motor drive 6, the pulse motor drive device 7, andthe interface device 10 shown in FIG. 8 in the embodiment.

An output from the interface device 10, which processes an output fromthe encoder 1507, that is, angular displacement information P301(i−1) ofthe rotating body 1505, is given to the arithmetic operation unit 304.The arithmetic operation unit 304 calculates a difference e(i) betweentarget angular displacement Ref(i) of the rotating body 1505, which is acontrol target value, and angular displacement P301(i−1) of the rotatingbody 1505. The arithmetic operation unit 304 inputs the difference e(i)to a controller unit 305.

The controller unit 305 is constituted by, for example, a PI controlsystem. The difference e(i) calculated in the arithmetic operation unit304 is integrated in the block 306, multiplied by a constant KI in ablock 307, and given to the arithmetic operation unit 308.Simultaneously, the difference e(i) calculated in the arithmeticoperation unit 304 is multiplied by a constant KP in the block 309 andgiven to the arithmetic operation unit 308. The arithmetic operationunit 308 adds two input signals from the blocks 307 and 309 and gives aresult of the addition to the feedback signal selecting unit 311. Thefeedback signal selecting unit 311 receives a feedback judgment signal,selects an output from the arithmetic operation unit 308 or a constant0, and gives the output or the constant 0 to the arithmetic operationunit 310. In short, the feedback signal selecting unit 311 selects theoutput from the arithmetic operation unit 308 when feedback is performedand selects the constant 0 when feedback is not performed. The feedbackjudgment signal can be given as, for example, an arbitrary I/O signalaffected by abnormality of a sensor or the like. It is needless tomention that the feedback signal selecting unit 311 selects the outputfrom the arithmetic operation unit 308 when there is no abnormality andselects the constant 0 when there is abnormality. Thereafter, thearithmetic operation unit 310 adds a constant pulse input Refp_c anddetermines a drive pulse frequency u(i).

The drive pulse frequency u(i) calculated in the arithmetic operationunit 310 is output to the pulse motor 1501 via the interface for pulsemotor drive 6 and the pulse motor drive device 7, the rotating body 1505rotates via a transmission system, and the loop operation describedabove is repeated. Although a PI control system is used as thecontroller unit 305 as an example, the controller unit 305 is notlimited to this. All the above-mentioned arithmetic operations areperformed by a numerical operation in the microcomputer 1 and can berealized easily.

Refp_c is a pulse number that is determined uniquely based on a driveroller angular velocity and a reduction gear ratio of a decelerationsystem that are based on a belt velocity and a belt drive radius.However, in the invention, it is also possible to select a pulse numberarbitrarily within a range in which a step-out phenomenon does not occurduring motor driving. In addition, Ref(i) can be calculated easily byintegrating a target uniform angular velocity of the driven roller 1510.

According to the third embodiment, when there is abnormality, usualpulse motor drive is performed without performing feedback. Thus, a beltconveyance control apparatus in a pulse motor drive system, which iscapable of carrying out accurate and highly accurate control even whenthere is a wrong output in a detection signal due to influence of noiseor the like caused by failure and abnormality in a sensor, can beestablished.

Next, a fourth embodiment of the invention will be explained. The fourthembodiment is an example of the belt conveyance control method.

In FIG. 10, reference numeral 1501 denotes a pulse motor serving as arotation drive source for driving to rotate the belt 1502. A rotationtorque of the pulse motor 1501 is transmitted to the drive shaft 1506and the drive roller 1505 for the belt by a deceleration system, forexample, the timing belt 1503 constituting the power transmissionsystem. The belt is wound around the drive roller 1505 and the drivenrollers 1510, 1511, 1512, 1513, and 1514. Therefore, when the driveroller 1505 is rotated by the pulse motor 1501, the belt 1502 movesaccordingly.

Reference numeral 1507 denotes a marker sensor set in a position opposedto a marker 1508. The marker sensor 1507 includes a photo-interrupter.The marker sensor 1507 outputs a digital signal “1” when the marker 1508reaches a detection position to be opposed to the marker sensor 1507 andoutputs a digital signal “0” when a part between the marker 1508 andanother marker 1508 reaches the detection position to be opposed to themarker sensor 1507. Displacement of the surface of the belt 1502 can bedetected by counting a digital signal from the marker sensor 1507.Although not shown in the figure, the marker 1508 necessarily has a gap,and the marker sensor 1507 cannot output a signal at a predeterminedinterval in that part.

A belt conveying apparatus shown in FIG. 10 is subjected to drivecontrol in a control system shown in FIGS. 11 and 12.

FIG. 11 shows a structure of a control system that subjects angulardisplacement of the pulse motor 1501 to digital control based on a statedetection signal for the belt 1502 (in this context, an output signal ofthe encoder 1507). In FIG. 11, reference numeral 1 denotes amicrocomputer including the microprocessor 2, and the read only memory(ROM) 3, the random access memory (RAM) 4. The microprocessor 2, theread only memory (ROM) 3, and the random access memory (RAM) 4 areconnected to one another via the bus 9.

Reference numeral 5 denotes an instruction generating device thatoutputs a state instruction signal for instructing target angulardisplacement of the belt 1502. The instruction generating device 5generates an angular displacement instruction signal. An output side ofthe instruction generating device 5 is also connected to the bus 9.Reference numeral 10 denotes an interface device for detection thatprocesses an output pulse of the marker sensor 1507 and converts theoutput pulse into a digital numerical value. The interface device fordetection 10 includes a counter that counts an output pulse of themarker sensor 1507. The interface device for detection 10 multiplies anumerical value counted by the counter by a predetermined conversionconstant of pulse number versus angular displacement and converts thenumerical value into displacement of the belt 1502. Reference numeral 6denotes an interface for pulse motor drive. The interface for pulsemotor drive 6 converts a result of arithmetic operation (control output)of the microcomputer 1 into a pulse-like signal (control signal) foractuating, for example, a power semiconductor constituting a pulse motordrive device 7. The pulse motor drive device 7 operates based on thepulse-like signal from the interface for pulse motor drive 6 and drivesto rotate the pulse motor. As a result, the belt 1502 is controlled tofollow up predetermined angular displacement instructed by theinstruction generating device 5. In other words, the belt 1502 is drivenat uniform velocity. The angular displacement of the belt 1502 isdetected by the encoder 1507 and the interface device 10 and taken intothe microcomputer 1, and these operations are repeated. Here, referencenumeral 11506 denotes a block indicating the belt conveying apparatus,and 11510 denotes a block indicating the timing belt power transmissionsystem 1503 shown in FIG. 10.

Next, drive control for a belt, which controls the belt to come into auniform angular velocity state by controlling rotation angledisplacement of the belt 1502 with the pulse motor 1501 according to theembodiment constituted as described above, will be explained withreference to a block structure of the embodiment shown in FIG. 12. InFIG. 12, reference numeral 801 denotes a control object including theentire drive system shown in FIG. 10 and the interface for pulse motordrive 6, the pulse motor drive device 7, and the interface device 10shown in FIG. 11 in the embodiment.

An output from the interface device 10, which processes an output fromthe marker sensor 1507, that is, displacement information P301(i−1) ofthe belt 1502, is given to the arithmetic operation unit 304. Thearithmetic operation unit 304 calculates a difference e(i) betweentarget angular displacement Ref(i) of the belt 1502, which is a controltarget value, and measured displacement P301(i−1) of the belt 1502. Thearithmetic operation unit 304 inputs the difference e(i) to a controllerunit 305.

The controller unit 305 is constituted by, for example, a PI controlsystem. The difference e(i) calculated in the arithmetic operation unit304 is integrated in the block 306, multiplied by a constant KI in ablock 307, and given to the arithmetic operation unit 308. At the sametime, the difference e(i) calculated in the arithmetic operation unit304 is multiplied by a constant KP in the block 309 and given to thearithmetic operation unit 308. The arithmetic operation unit 308 addstwo input signals from the blocks 307 and 309 and gives a result of theaddition to the feedback signal selecting unit 311. The feedback signalselecting unit 311 receives a feedback judgment signal, selects anoutput from the arithmetic operation unit 308 or a constant 0, and givesthe output or the constant 0 to the arithmetic operation unit 310. Inshort, the feedback signal selecting unit 311 selects the output fromthe arithmetic operation unit 308 when feedback is performed and selectsthe constant 0 when feedback is not performed. The feedback judgmentsignal can be given as, for example, an arbitrary I/O signal affected bya gap of a marker sensor, abnormality of a sensor, or the like. It isneedless to mention that the feedback signal selecting unit 311 selectsthe output from the arithmetic operation unit 308 when there is noabnormality and selects the constant 0 when there is abnormality.Thereafter, the arithmetic operation unit 310 adds a constant pulseinput Refp_c and determines a drive pulse frequency u(i).

The drive pulse frequency u(i) calculated in the arithmetic operationunit 310 is output to the pulse motor 1501 via the interface for pulsemotor drive 6 and the pulse motor drive device 7, the drive shaft 1505rotates via a transmission system, and the loop operation describedabove is repeated. Although a PI control system is used as thecontroller unit 305 as an example, the controller unit 305 is notlimited to this. All the above-mentioned arithmetic operations areperformed by a numerical operation in the microcomputer 1 and can berealized easily.

Refp_c is a pulse number that is determined uniquely based on a driveroller angular velocity and a reduction gear ratio of a decelerationsystem that are based on a belt velocity and a belt drive radius.However, in the invention, it is also possible to select a pulse numberarbitrarily within a range in which a step-out phenomenon does not occurduring motor driving. In addition, Ref(i) can be calculated easily byintegrating a target uniform angular velocity of the driven roller 1510.

According to the fourth embodiment, when there is a gap of a markersensor, abnormality of a sensor, or the like, usual pulse motor drive isperformed without performing feedback. Thus, a belt conveyance controlapparatus in a control system for a pulse motor using a belt surfacesensor, which is capable of carrying out correct and highly accuratecontrol even when there is a wrong output in a detection signal due toinfluence of noise or the like caused by a gap of a marker sensor orfailure and abnormality in a sensor, can be established.

Next, a fifth embodiment of the invention will be explained. Althoughthe fifth embodiment will be explained using the first embodiment, theinvention is applicable to the second embodiment to the fourthembodiment in the same manner.

FIG. 13 is a structure of a control system that controls the rotatingbody 1505 to come into a uniform angular velocity state by controllingrotation angle displacement of the rotating body 1505 with the pulsemotor 1501. In FIG. 13, reference numerals and signs identical withthose in FIG. 3 denote the identical components, and an explanation ofthe components will be omitted.

A difference e(i) between a target angular displacement Ref(i) of therotating body 1505 and angular displacement P301(i−1) of the rotatingbody 1505 is input to the controller unit 401. The controller unit 401includes only a system without an integrating element, for example, aproportional control system. A result of an arithmetic operation isgiven to the arithmetic operation unit 310, a constant pulse inputRefp_c is added to the result in the arithmetic operation unit 310, anda drive pulse frequency u(i) is determined.

If an integrating element is included in the control system, when afeedback pulse is added or is not added to a drive pulse, the drivepulse may include a large error depending upon timing for the switching.Thus, to avoid such a risk, the control system is established by asystem not including an integrating element. The control system is notlimited to a proportional control system and may be any system as longas an integrating element is not included.

According to the fifth embodiment, since the feedback system isestablished by a system not including an integrating element, a positioncontrol system in a pulse motor drive system, which is capable ofcarrying out correct and highly accurate control even when there is awrong output in a detection signal due to influence of noise or the likecaused by failure or abnormality of a sensor, can be established moresafely.

A seventh embodiment of the invention will be hereinafter explained withreference to FIGS. 14 to 22.

First, with reference to FIG. 14, a basic structure of a belt driveapparatus including a belt serving as a rotating body to be an object ofposition control (drive control) will be explained. The belt is anendless belt wound around at least two shafts and is equivalent to aphotosensitive belt, an intermediate transfer belt, and a directtransfer belt to be described later.

A drive shaft 2101 is attached to a rotation shaft of a gear 2100 to becapable of rotating synchronously with the rotation shaft. A gear 2103is attached to a rotation shaft of a motor 2102 to transmit rotation ofthe motor 2102 serving as a drive source via a gear 2103 and a gear 2100and drive to rotate the drive shaft 2101. A belt 2106, which is anobject of drive and an object of position control, is wound around thedrive shaft 2101 and driven shafts 2104 and 2105 such that a constanttension is applied to the belt 2106 by a tension roller 2107.

A linear scale 2108 serving as a scale is stuck on a surface of the belt2106 along a moving direction of the belt 2106. This linear scale 2108is read by a surface sensor 2109 consisting of a reflectivephoto-sensor, whereby a drive state (fluctuation in velocity) of thebelt 2106 is measured. The linear scale 2108 and the surface sensor 2109constitute a signal generating unit.

The belt 2106, which is the object of drive, is driven to rotate byrotating the motor 2102. Although the linear scale 2108 is stuck at anend on the surface of the belt 2106 here, the linear scale 2108 may bestuck in a central part or on a back of the belt 2106. In addition, ascale may be written on the belt 2106 directly.

A basic structure of a rotating body drive apparatus including arotating body to be an object of position control will be explained withreference to FIG. 15. The rotating body is equivalent to aphotosensitive drum and a transfer drum to be described later.

A drive pulley 2125 is attached to a rotation shaft 2124 of a gear 2122.A gear 2123 engaging with the gear 2122 is attached to a rotation shaftof a motor 2121 serving as a drive source. The drive pulley 2125 isdriven to rotate by rotation of the motor 2121.

A motor shaft encoder 2129 is attached to the motor 2121. A timing belt2131 is wound around the drive pulley 2125 and a driven pulley 2128 suchthat a constant tension is applied to the timing belt 2131 by a tensionpulley 2130. A drum 2126 serving as a rotating body, which is an objectof drive and an object of position control, is attached to the drivenpulley 2128 via a shaft 2127 such that coaxiality is kept. A linearscale 2108 serving as a scale is stuck on a surface of the drum 2126,which is the object of drive, along a peripheral direction thereof. Thelinear scale 2108 is read by the surface sensor 2109, whereby a drivestate (fluctuation in velocity) of the drum 2126 is measured.

The drum 2126 is driven to rotate by rotating the motor 2121. The linearscale 2108 is stuck to an end of the surface of the drum 2126 as well inthis structure. However, the linear scale 2108 may be stuck in a centralpart of the surface of the drum 2126 or, if the drum 2126 is tubular,may be stuck on a back thereof. In addition, a scale may be written onthe drum 2126 directly. Any object may be used instead of a scale aslong as positional displacement (drive displacement) of a rotating bodycan be grasped as some signal amount using the object.

FIG. 16 is an enlarged view of a joint part of the linear scale 2108that is stuck to the belt 2106 in FIG. 14 or the drum 2126 in FIG. 15.Patterns (reference graduations for signal and pulse generation) 2108 a,which make it possible to measure a drive state, are written in thelinear scale 2108 at equal intervals in a moving direction of a rotatingbody by a method like laser irradiation.

More specifically, the patterns 2108 a are written on a tape made ofaluminum, and light emitted from a not-shown light-emitting element ofthe surface sensor 2109 is irradiated on the linear scale 2108 andreflected, and a not-shown light-receiving element of the surface sensor2109 detects the reflected light. Since the reflected light is intensein parts where the patterns 2108 a are not written and the reflectedlight is weak in parts where the patterns 2108 a are written, thepatterns 2108 a of the linear scale 2108 is recognized. Although analuminum tape is used as a base material of the linear scale 2108 here,a tape of other materials may be used as long as a drive state can bemeasured.

There are two kinds of joints in a method of sticking a tape-like scalesuch as the linear scale 2108. One is a physical joint 2132 where thelinear scale 2108 is not physically continuous as shown in FIG. 16A. Theother is a writing joint 2133 as a blank part, where nothing is writtenon the linear scale 2108 because of a problem of accuracy or the like atthe time when the patterns 2108 a are written, although the linear scale2108 is present continuously as shown in FIG. 16B.

There is no tape at all in the physical joint 2132, and only a tapewithout the patterns 2108 a is present in the writing joint 2133. Thus,a usual measurement signal is not obtained in both the joints.Therefore, in this embodiment, these joints are treated as the samejoints and will be hereinafter expressed simply as “joint”. In thisexplanation, it is assumed that the physical joint 2123 and the writingjoint 2133 are present separately. However, the physical joint 2123 andthe writing joint 2133 may be treated as joints even if the physicaljoint 2123 and the writing joint 2133 are mixed. In addition, a usualmeasurement signal is not obtained due to an output error of the surfacesensor 2109 itself including scratches, stains, and noise as in thejoints.

FIG. 17 is a block diagram of a structure of a control system thatsubjects angular displacement of the motor 2121 to digital control basedon an output signal of the motor shaft encoder 2129 in a current controlsystem common to the respective embodiments.

In FIG. 17, reference numeral 2135 denotes a microcomputer including amicroprocessor 2136, a read only memory (ROM) 2137, and a random accessmemory (RAM) 2138. The microprocessor 2136, the read only memory (ROM)2137, and the random access memory (RAM) 2138 are connected to oneanother via a bus 2143.

Reference numeral 2139 denotes an instruction generating device thatoutputs a state instruction signal for instructing angular displacementof the motor 2121. The instruction generating device 2139 generates atarget angular displacement instruction signal. An output side of theinstruction generating device 2139 is also connected to the bus 2143.Reference numeral 2142 denotes an interface device for detection thatprocesses an output pulse of a motor shaft encoder 2129 and converts theoutput pulse into a digital numerical value. The interface device fordetection 2142 includes a counter that counts an output pulse of themotor shaft encoder 2129. The interface device for detection 2142multiplies a numerical value counted by the counter by a predeterminedconversion constant of pulse number versus angular displacement andconverts the numerical value into angular displacement of a motor shaft.A motor drive current is taken into the microcomputer 2135 from acurrent sensor 2144 via an I/O 2145.

Reference numeral 2140 denotes an interface for DC motor drive. Theinterface for DC motor drive 2140 converts a calculation result of afeedback control system, which is described in embodiments to bedescribed later, obtained by the microcomputer 2135 into a pulse-likesignal (control signal) for actuating a power semiconductor, forexample, a transistor constituting a motor (DC motor) drive device 2141according to motor shaft angular displacement and target angulardisplacement.

The DC motor drive device 2141 operates based on the pulse-like signalfrom the interface for DC motor drive 2140 and controls a voltage to beapplied to the motor 2121. As a result, the motor 2121 is controlled tofollow up predetermined angular displacement instructed by theinstruction generating device 2139. Angular displacement of the motor2121 is detected by the motor shaft encoder 2129 and the interfacedevice 2142 and taken into the microcomputer 2135, and the control isrepeated.

The linear scale 2108, the surface sensor 2109, and the microcomputer2135 serving as control means constitute a position control device thatcontrols position of a rotating body in this embodiment.

FIG. 18 is a block diagram of a structure of a control system thatmeasures angular velocity of the motor 2121 while subjecting angulardisplacement of the motor 2121 to digital control based on an outputsignal of the motor shaft encoder 2129 in a current control systemcommon to the respective embodiments.

Only differences from the structure shown in FIG. 17 will be explained.A device 2147 for detecting angular velocity of the motor 2121 isattached to the motor 2121, an output from the device 2147 is input tothe interface device 2145 for detection, which converts the output intoa digital numerical value, and motor drive velocity is taken into themicrocomputer 2135.

Here, angular displacement is detected by an encoder or the likedirectly from the motor 2121. The same holds true for a method ofdetecting drive of the belt 2106 and the drum 2126 driven by the motor2102 and the motor 2121.

In an explanation of this embodiment, an output error of the surfacesensor 2109 itself including noise like a joint and dust has occurredand a signal amount (scale pulse number) read in sampling time hasfallen below a defined pulse count number (hereinafter simply referredto as “pulse number” as well).

FIG. 19 is a diagram of a drive state at the time when the motor 2102 orthe motor 2121 is rotated and driven with respect to the belt 2106 inFIG. 14 or the drum 2126 in FIG. 15. In FIG. 19, a horizontal axisindicates time and a vertical axis indicates a pulse count number persampling time measured by the surface sensor 2109 (the same holds truefor graphs to be described below).

Before explaining characteristics of this embodiment, usual drivecontrol, which has been performed conventionally, will be explained withreference to a part of FIG. 19 and a feedback control system shown inFIG. 20. The pulse number per sampling time fluctuates within a range ofa usual area a1 in FIG. 19 due to a usual disturbance. At this point, asshown in FIG. 20, in the feedback control system, a control signal isoutput from a controller 2150, and a drive source of a plant 2151 isdriven in response to the control signal. Here, the controller 2150 alsoincludes a current control loop, and the plant 2151 means an overallstructure (drive device) that drives the belt 2106 and the drum 2126with the motors 2102 and 2121 shown in FIGS. 14 and 15.

The surface sensor 2109 measures a drive state of a rotating body suchas the belt 2106 and the drum 2126, and an accumulated signal value 2152is obtained. This accumulated signal value 2152 is feedbacked, asubtracter 2154 compares the fed-back accumulated signal value 2152 anda reference signal 2153 to calculate a deviation 2155 between presentdisplacement and target displacement.

This deviation 2155 is input to the controller 2150, whereby a newcontrol signal is created. This is the usual control that has beenperformed conventionally. Conventionally, feedback control has beenperformed based on only fluctuation in the range of the usual area a1 inFIG. 19. In other words, the control is performed according to judgmenton whether there is a signal.

This embodiment will be hereinafter explained specifically. A pulsenumber at present sampling time can be calculated as, for example,(present accumulated pulse number)—(accumulated pulse number atimmediately preceding sampling time) from the accumulated signal value2152 measured by the surface sensor 2109. The pulse number at thepresent sampling time is calculated in this way.

As shown in FIG. 19, this embodiment introduces a concept of dividing anarea where a signal (scale pulse) is generated into the usual area a1where a fluctuation width, which could occur due to usual disturbance,is taken into account and au unusual area a2 deviating from the usualarea a1. A pulse number range equivalent to fluctuation, which hardlyoccurs due to usual disturbance, that is, the unusual area a2 outsidethe range of the usual area a1 is determined.

Then, when a signal enters this unusual area a2, it is determined thatan error has occurred.

A designer can determine the usual area a1 arbitrarily. As an example ofa method of determining a threshold pulse number, when it is assumedthat sampling time is A, velocity of the belt 2106 is B, resolution isC, and a scale pitch (pitch of patterns 2108 a) is D, the designercalculates a theoretical value as A×B×C÷D, determines a fluctuationwidth, which could occur due to usual disturbance, with respect to thisvalue, and further determines the usual area a1 shown in FIG. 19 takinginto account a margin equivalent to the fluctuation range. “Margin” inthis context can be determined from, for example, a distribution stateof experimental data.

When only a usual feedback control is performed, as described above, thecontrol is performed based on a measurement result like a pulse numberPn3 in the range of the usual area a1 in FIG. 19.

However, when an output error of the surface sensor 2109 itselfincluding noise like a joint and dust has occurred, the measured pulsenumber changes to Pn4. Then, although the belt 2106 or the drum 2126 isdriven normally, a pulse number is not measured, or a pulse number ismeasured as if the pulse number has decreased. It is judged that drivingof the belt 2106 or the drum 2126 has slowed down.

Therefore, a signal instructing to increase velocity is sent from thecontrol side. Then, when the error part ends (passes) and the measuredpulse number changes to Pn6, it is judged that driving of the belt 2106or the drum 2126 is fast because the velocity is increased in the errorpart, and a signal instructing to decrease velocity is sent from thecontrol side. Through the series of processing, fluctuation, which isnot present originally, is caused by the output error of the surfacesensor 2109 itself, and large fluctuation is caused in driving of thebelt 2106 or the drum 2126.

It is also likely that the control system becomes unstable whenmeasurement time for an error is long or error occurs frequently, andcontinuation of control becomes impossible.

Consequently, it is necessary to perform error detection for the pulsenumber Pn4 or the like, which is measured in the error partinadvertently, and further perform error correction to prevent thecontrol system from being made unstable.

Thus, this embodiment is characterized in that, when it is judged that ameasured pulse number is an error, control is continued using a definedpulse number (dummy pulse number) within the usual area a1 instead ofthe measured pulse number.

This embodiment is different from the conventional technique in that allsignals deviating from the usual area a1 where a fluctuation width,which could occur due to a usual disturbance, is taken into account arecaptured and subjected to correction processing to be used for control.

FIG. 21 shows the control system in this embodiment. The controller 2150outputs a control signal, and a drive source for the plant 2151 isdriven by the control signal. The accumulated signal value 2152 isobtained from the surface sensor 2109 that has measured a drive state ofthe plant 2151, and the value is input to a correction processing unit2156.

If a measured value is a usual value, that is, a pulse number is withinthe usual area a1, the correction processing unit 2156 outputs the valuedirectly as a feedback signal. If it is judged that the measured valueis an error, that is, the pulse number is within the unusual area a2,the correction processing unit 2156 feedbacks a value subjected tocorrection processing.

The subtracter 2154 compares the feedback value from the correctionprocessing unit 2156 and the reference signal 2153 and inputs adeviation between the feedback value and the reference signal 2153 to aswitching unit 2157. When the correction processing unit 2156 judges themeasured value is a usual value, the switching unit 2157 uses thedeviation directly as a control input. When the correction processingunit 2156 judges that the measured value is an error, a signalgenerating unit 2158 inputs zero to the switching unit 2157 as a controlinput.

In the control system in FIG. 21, the entire control system excludingthe plant 2151 constitutes the microcomputer 2135 as a control unit inthis embodiment.

An example of a method of determining a dummy pulse number used in thecorrection processing will be explained with reference to FIG. 22. Theusual feedback control is performed up to the pulse number Pn3. Whilethe control is performed, a pulse number in sampling time at that pointis saved in, for example, the RAM 2138. When signals from the surfacesensor 2109 are normal continuously (when the signals are within theusual area a1), a value of a pulse number is always rewritten, that is,updated.

Then, when the pulse number Pn4 is measured, since the pulse number Pn4is within the unusual area a2 where a pulse number does not satisfy thedefined pulse number, the microcomputer 2135 judges that the pulsenumber Pn4 is an error.

Consequently, the pulse number saved in the RAM 2138 when the signalsare normal (the pulse number Pn3 updated last) is used as a dummy pulsenumber in error processing instead of the pulse number Pn4. A pulsenumber Pn4 a is treated as a measured pulse number in a control loop.The same holds true for a pulse number Pn5.

When a pulse number enters the error part, the saved pulse number is notupdated. An error is always corrected using the saved pulse number (thepulse number Pn3 updated last) in the error part. This processing iscontinued while a pulse number is judged as an error.

When the error part ends and a pulse number Pn6 is measured, the controldeparts from the error processing, the usual feedback control isperformed, and the saved pulse number is updated again. In this way, thecontrol system does not become unstable to continue the control. Here, apulse number to be saved may be a pulse number in sampling of the lasttime or much earlier sampling.

An eighth embodiment of the invention will be explained with referenceto FIG. 23. Note that, components identical with those in theabove-mentioned embodiment are denoted by the identical referencenumerals. The structures and the functions already explained will not beexplained repeatedly unless specifically required, and only principalparts will be explained (the same holds true for other embodiments to bedescribed later).

As shown in FIG. 23, the usual feedback control is performed up to apulse number Pn12. When a pulse number Pn13 is measured, since the pulsenumber Pn13 is within the unusual area a2 where a pulse number does notsatisfy the defined pulse, the pulse number Pn13 is judges as an error.

In this case, a calculated logical pulse number is used as a dummy pulsenumber instead of the pulse number Pn13. A logical pulse number Pn13 ais treated as a measured pulse number in the control loop. The sameholds true for a pulse number Pn14. This processing is continued while apulse number is judged as an error. When the error part ends and a pulsenumber Pn15 is measured, the control departs from the error processing,and the usual feedback control is performed. In this way, the controlsystem does not become unstable to continue the control.

A ninth embodiment of the invention will be explained with reference toFIG. 24.

The usual feedback control is performed up to a pulse number Pn24. Inthe usual feedback control, at least two pulse numbers in sampling timein the past are saved. In this embodiment, a case in which five pulsenumbers are saved will be considered.

When signals from the surface sensor 2109 are normal continuously, avalue saved earliest is always rewritten such that a state in whichimmediately preceding five pulse numbers are always saved is maintained.Then, when a pulse number Pn25 is measured, since the pulse number Pn25is within the unusual area a2 where a pulse number does not satisfy thedefined pulse, the pulse number Pn25 is judged as an error.

An average value of the saved immediately preceding five pulse numbersis used as a dummy pulse number instead of the pulse number Pn25. Apulse number Pn25 a is treated as a measured pulse number in the controlloop. The same holds true for a pulse number Pn26.

When a pulse number is in the error part, the pulse number is notupdated. While the pulse number is in the error part, an error is alwayscorrected using the average value calculated earlier. This processing iscontinued while a pulse number is judged as an error. When the errorpart ends and a pulse number Pn27 is measured, the control departs fromthe error processing, the usual feedback control is performed, and thesaved pulse number is updated. In this way, the control system does notbecome unstable to continue the control.

A tenth embodiment of the invention will be explained with reference toFIG. 25.

The usual feedback control is performed up to a pulse number Pn34. Inthe usual feedback control, average velocity of a rotating body insections in the past is calculated, and an average pulse number iscalculated from the average velocity and saved. When signals from thesurface sensor 2109 are normal continuously, a value of the averagepulse number calculated from the average velocity is always updatedcontinuously.

When a pulse number Pn35 is measured, since the pulse number Pn35 iswithin the unusual area a2 where a pulse number does not satisfy thedefined pulse number, the pulse number Pn35 is judges as an error. Theaverage pulse number calculated from the average velocity is used as adummy pulse number instead of the pulse number Pn35. A pulse number Pn35a is treated as a measured pulse number in the control loop. The sameholds true for a pulse number Pn36.

When a pulse number is in the error part, the saved average pulse numbercalculated from the average velocity is not updated. While the pulsenumber is in the error part, an error is always corrected using theaverage pulse number. This processing is continued while a pulse numberis judged as an error. When the error part ends and a pulse number Pn37is measured, the control departs from the error processing, the usualfeedback control is performed, and a value of the average pulse numbercalculated from the average velocity is updated again. In this way, thecontrol system does not become unstable to continue the control.

According to the respective embodiments, a position accuracy of drivingof the belt 2106 or the drum 2126, which is an object of drive, can beimproved, and highly accurate driving can be performed.

In the explanation of all the embodiments, an output error of thesurface sensor 2109 itself including a joint, dust, and noise hasoccurred and a pulse number has fallen below the defined pulse number.In an explanation of an eleventh embodiment, a signal amount (scalepulse number) read in sampling time has exceeded the defined pulsenumber.

As shown in FIG. 26, an area where a signal (scale pulse) is generatedis divided into a usual area a1 where a fluctuation width, which couldoccur due to usual disturbance, is taken into account and an unusualarea a3 deviating from the usual area a1. When a signal enters thisunusual area a3, it is determined that the signal is an error. A methodof determining the usual area a1, a method of determining a thresholdpulse number, and the like are the same as those in the abovedescription.

When only the usual feedback control is performed, the control isperformed based on a measurement result of a pulse number Pn40 and thelike in a range of the usual area a1.

However, when an output error of the surface sensor 2109 itselfincluding a joint, dust, and noise occurs, a measured pulse numberchanges to Pn43. Then, although the belt 2106 or the drum 2126 is alwaysdriven, a pulse number is not measured, or a pulse number is measured asif the pulse number has decreased. It is judged that driving of the belt2106 or the drum 2126 has slowed down.

Therefore, a signal instructing to increase velocity is sent from thecontrol side. Then, when the error part ends (passes) and the measuredpulse number changes to Pn45, it is judged that driving of the belt 2106or the drum 2126 is fast because the velocity is increased in the errorpart, and a signal instructing to decrease velocity is sent from thecontrol side. Through the series of processing, fluctuation, which isnot present originally, is created by the output error of the surfacesensor 2109 itself, and large fluctuation is caused in driving of thebelt 2106 or the drum 2126.

It is also likely that the control system becomes unstable whenmeasurement time for an error is long or error occurs frequently, andcontinuation of control becomes impossible.

Consequently, it is necessary to perform error detection for the pulsenumber Pn43 or the like, which is measured in the error partinadvertently, and further perform error correction to prevent thecontrol system from being made unstable.

Thus, in this embodiment, when it is judged that a measured pulse numberis an error, control is continued using a defined pulse number (dummypulse number) within the usual area a1 instead of the measured pulsenumber. The control system at the time when the correction processing isperformed is the same as that in the above-mentioned embodiments.

An example of a method of determining a dummy pulse number used in thecorrection processing will be explained with reference to FIG. 27.

The usual feedback control is performed up to a pulse number Pn52. Whilethe control is performed, a pulse number in sampling time at that pointis saved. When signals from the surface sensor 2109 are normalcontinuously, a value of a pulse number is always rewritten.

When a pulse number Pn53 is measured, since the pulse number Pn53 iswithin the unusual area a3 where a pulse number does not satisfy thedefined pulse number, it is judged that the pulse number Pn53 is anerror. Thus, the pulse number Pn52, which is saved when the signals arenormal, is used as a dummy pulse number in error processing instead ofthe pulse number Pn53. A pulse number Pn53 a is treated as a measuredpulse number in a control loop. The same holds true for a pulse numberPn54.

When a pulse number is in the error part, the saved pulse number is notupdated. An error is always corrected using the saved pulse number inthe error part. This processing is continued while a pulse number isjudged as an error. When the error part ends and a pulse number Pn55 ismeasured, the control departs from the error processing, the usualfeedback control is performed, and the saved pulse number is updatedagain. In this way, the control system does not become unstable tocontinue the control. Here, a pulse number to be saved may be a pulsenumber in sampling of the last time or much earlier sampling.

A twelfth embodiment of the invention will be explained with referenceto FIG. 28.

The usual feedback control is performed up to a pulse number Pn62. Whena pulse number Pn63 is measured, since the pulse number Pn63 is withinthe unusual area a3 where a pulse number does not satisfy the definedpulse, the pulse number Pn63 is judges as an error. A calculated logicalpulse number is used as a dummy pulse number instead of the pulse numberPn63. A logical pulse number Pn63 a is treated as a measured pulsenumber in the control loop. The same holds true for a pulse number Pn64.

This processing is continued while a pulse number is judged as an error.When the error part ends and a pulse number Pn65 is measured, thecontrol departs from the error processing, and the usual feedbackcontrol is performed. In this way, the control system does not becomeunstable to continue the control.

A thirteenth embodiment of the invention will be explained withreference to FIG. 29.

The usual feedback control is performed up to a pulse number Pn74. Inthe usual feedback control, at least two pulse numbers in sampling timein the past are saved. In this embodiment, a case in which five pulsenumbers are saved will be considered.

When signals from the surface sensor 2109 are normal continuously, avalue saved earliest is always rewritten such that a state in whichimmediately preceding five pulse numbers are always saved is maintained.Then, when a pulse number Pn75 is measured, since the pulse number Pn75is within the unusual area a3 where a pulse number does not satisfy thedefined pulse, the pulse number Pn75 is judged as an error. An averagevalue of the saved immediately preceding five pulse numbers is used as adummy pulse number instead of the pulse number Pn75. A pulse number Pn75a is treated as a measured pulse number in the control loop. The sameholds true for a pulse number Pn76.

When a pulse number is in the error part, the pulse number is notupdated. While the pulse number is in the error part, an error is alwayscorrected using the average value calculated earlier. This processing iscontinued while a pulse number is judged as an error. When the errorpart ends and a pulse number Pn77 is measured, the control departs fromthe error processing, the usual feedback control is performed, and thesaved pulse number is updated. In this way, the control system does notbecome unstable to continue the control.

A fourteenth embodiment of the invention will be explained withreference to FIG. 30.

The usual feedback control is performed up to a pulse number Pn84. Inthe usual feedback control, average velocity of a rotating body insections in the past is calculated, and an average pulse number iscalculated from the average velocity and saved. When signals from thesurface sensor 2109 are normal continuously, a value of the averagepulse number calculated from the average velocity is always updatedcontinuously.

When a pulse number Pn85 is measured, since the pulse number Pn85 iswithin the unusual area a3 where a pulse number does not satisfy thedefined pulse number, the pulse number Pn85 is judges as an error. Theaverage pulse number calculated from the average velocity is used as adummy pulse number instead of the pulse number Pn85. A pulse number Pn85a is treated as a measured pulse number in the control loop. The sameholds true for a pulse number Pn86.

When a pulse number is in the error part, the average pulse numbercalculated from the average velocity is not updated. While the pulsenumber is in the error part, an error is always corrected using theaverage pulse number. This processing is continued while a pulse numberis judged as an error. When the error part ends and a pulse number Pn87is measured, the control departs from the error processing, the usualfeedback control is performed, and a value of the average pulse numbercalculated from the average velocity is updated again. In this way, thecontrol system does not become unstable to continue the control.

As described above, a position accuracy of driving of the belt 2106 orthe drum 2126, which is an object of drive, can be improved, and highlyaccurate driving can be performed.

In the explanation of the above-mentioned respective embodiments, apulse number has fallen below the defined pulse number or the case inwhich a pulse number has exceeded the defined pulse number. In anexplanation of a fifteenth embodiment, an output error of the surfacesensor 2109 itself including a joint, dust, and noise occurs and asignal amount (scale pulse number) read in sampling time exceeds orfalls below the defined pulse number.

As shown in FIG. 31, an area where a signal (scales pulse) is generatedis divided into a usual area a1 where a fluctuation width, which couldoccur due to usual disturbance, is taken into account, and an unusualarea a2 and an unusual area a3 deviating from the usual area a1. When asignal enters the unusual area a2 or a3, it is determined that thesignal is an error. A method of determining the usual area a1, a methodof determining a threshold pulse number, and the like are the same asthose described above.

When only the usual feedback control is performed, the control isperformed based on a measurement result for a pulse number Pn90 within arange of the usual area a1.

However, when an output error of the surface sensor 2109 including ajoint, dust, and noise occurs, a measured pulse number changes to Pn93.Then, although the belt 2106 or the drum 2126 is driven normally, apulse number is not measured, or a pulse number is measured as if thepulse number has decreased. It is judged that driving of the belt 2106or the drum 2126 has slowed down.

When the measured pulse number changes to a pulse number Pn95, a pulsenumber is measured as if the measured number has increased, and it isjudged that driving of the belt 2106 or the drum 2126 has become fast.Therefore, a signal instructing to increase or decrease velocity is sentfrom the control side. Then, when the error part ends and the measuredpulse number changes to a pulse number Pn96, it is judged that drivingof the belt 2106 or the drum 2126 is fast because velocity is increasedin the error part as a whole or driving of the belt 2106 or the drum2126 is slow because velocity is decreased in the error part as a whole.A signal instructing to decrease or increase velocity is sent from thecontrol side.

Through the series of processing, fluctuation, which is not presentoriginally, is created by the output error of the surface sensor 2109itself, and large fluctuation is caused in driving of the belt 2106 orthe drum 2126.

It is also likely that the control system becomes unstable whenmeasurement time for an error is long or error occurs frequently, andcontinuation of control becomes impossible.

Consequently, it is necessary to perform error detection for the pulsenumber Pn93 and the pulse number Pn94, which is measured in the errorpart inadvertently, and further perform error correction to prevent thecontrol system from being made unstable.

Thus, in this embodiments, when it is judged that a measured pulsenumber is an error, control is continued using a defined pulse number(dummy pulse number) within the usual area a1 instead of the measuredpulse number. The control system at the time when n the correctionprocessing is performed is the same as that in the above-mentionedembodiments.

An example of a method of determining a dummy pulse number used in thecorrection processing will be explained with reference to FIG. 32.

The usual feedback control is performed up to a pulse number Pn2102.While the control is performed, a pulse number in sampling time at thatpoint is saved. When signals from the surface sensor 2109 are normalcontinuously, a value of a pulse number is always rewritten.

When a pulse number Pn2103 is measured, since the pulse number Pn2103 iswithin the unusual area a2 where a pulse number does not satisfy thedefined pulse number, it is judged that the pulse number Pn2103 is anerror. Thus, a pulse number, which is saved when the signals are normal,is used as a dummy pulse number in error processing. A pulse numberPn2103 a is treated as a measured pulse number in a control loop. Thesame holds true for a pulse number Pn2104.

When a pulse number is in the error part, the saved pulse number is notupdated. An error is always corrected using the saved pulse number inthe error part. In addition, when a pulse number Pn2105 is measuredcontinuously or discontinuously, since the pulse number Pn2105 is withinthe unusual area a3 where a pulse number does not satisfy the definedpulse number, the pulse number Pn2105 is judged as an error. In thiscase, as in the above case, a pulse number Pn2105 a is treated as ameasured pulse number in the control loop.

This processing is continued while a pulse number is judged as an error.When the error part ends and a pulse number Pn2106 is measured, thecontrol departs from the error processing, the usual feedback control isperformed, and the saved pulse number is updated again. In this way, thecontrol system does not become unstable to continue the control. Here, apulse number to be saved may be a pulse number in sampling of the lasttime or much earlier sampling.

A sixteenth embodiment of the invention will be explained with referenceto FIG. 33.

The usual feedback control is performed up to a pulse number Pn112. Whena pulse number Pn113 is measured, since the pulse number Pn113 is withinthe unusual area a2 where a pulse number does not satisfy the definedpulse, the pulse number Pn113 is judges as an error. A calculatedlogical pulse number is used as a dummy pulse number instead of thepulse number Pn113. A pulse number Pn113 a is treated as a measuredpulse number in the control loop. The same holds true for a pulse numberPn114.

When a pulse number Pn115 is measured continuously or discontinuously,since the pulse number Pn115 is within the unusual area a3 where a pulsenumber does not satisfy the defined pulse, the pulse number Pn115 isjudges as an error. In this case, as in the above case, a pulse numberPn115 a is treated as a measured pulse number in the control loop. Thisprocessing is continued while a pulse number is judged as an error.

When the error part ends and a pulse number Pn116 is measured, thecontrol departs from the error processing, and the usual feedbackcontrol is performed. In this way, the control system does not becomeunstable to continue the control.

A seventeenth embodiment of the invention will be explained withreference to FIG. 34.

The usual feedback control is performed up to a pulse number Pn2123. Inthe usual feedback control, at least two pulse numbers in sampling timein the past are saved. In this embodiment, a case in which four pulsenumbers are saved will be considered.

When signals from the surface sensor 2109 are normal continuously, avalue saved earliest is always rewritten such that a state in whichimmediately preceding four pulse numbers are always saved is maintained.

When a pulse number Pn2124 is measured, since the pulse number Pn2124 iswithin the unusual area a2 where a pulse number does not satisfy thedefined pulse, the pulse number Pn2124 is judged as an error. An averagevalue of the saved immediately preceding four pulse numbers is used as adummy pulse number instead of the pulse number Pn2124. A pulse numberPn2124 a is treated as a measured pulse number in the control loop. Thesame holds true for a pulse number Pn2125.

When a pulse number is in the error part, the saved pulse number is notupdated. While the pulse number is in the error part, an error is alwayscorrected using the average value calculated earlier. In addition, whena pulse number Pn2126 is measured continuously or discontinuously, sincethe pulse number Pn2126 is within the unusual area a3 where a pulsenumber does not satisfy the defined pulse number, the pulse numberPn2126 is judged as an error. In this case, as in the above case, apulse number Pn2126 a is treated as a measured pulse number in thecontrol loop.

This processing is continued while a pulse number is judged as an error.When the error part ends and a pulse number Pn2127 is measured, thecontrol departs from the error processing, the usual feedback control isperformed, and the saved pulse number is updated. In this way, thecontrol system does not become unstable to continue the control.

An eighteenth embodiment will be explained with reference to FIG. 35.

The usual feedback control is performed up to a pulse number Pn2123. Inthe usual feedback control, average velocity of a rotating body insections in the past is calculated, and an average pulse number iscalculated from the average velocity and saved. When signals from thesurface sensor 2109 are normal continuously, a value of the averagepulse number calculated from the average velocity is always updatedcontinuously.

When a pulse number Pn2134 is measured, since the pulse number Pn2134 iswithin the unusual area a2 where a pulse number does not satisfy thedefined pulse number, the pulse number Pn2134 is judges as an error. Theaverage pulse number calculated from the average velocity is used as adummy pulse number instead of the pulse number Pn2134. A pulse numberPn2134 a is treated as a measured pulse number in the control loop. Thesame holds true for a pulse number Pn2135.

When a pulse number is in the error part, the average pulse numbercalculated from the average velocity is not updated. While the pulsenumber is in the error part, an error is always corrected using theaverage pulse number. Moreover, when a pulse number Pn2136 is measuredcontinuously or discontinuously, since the pulse number Pn2136 is withinthe unusual area a3 where a pulse number does not satisfy the definedpulse number, the pulse number Pn2136 is judged as an error. In thiscase, as in the above case, a pulse number Pn2136 a is treated as ameasured pulse number in the control loop.

This processing is continued while a pulse number is judged as an error.When the error part ends and a pulse number Pn2137 is measured, thecontrol departs from the error processing, the usual feedback control isperformed, and a value of the average pulse number calculated from theaverage velocity is updated again. In this way, the control system doesnot become unstable to continue the control.

As described above, even when a pulse number falls below or exceeds thedefined pulse number, a position accuracy of driving of the belt 2106 orthe drum 2126, which is an object of drive, can be improved, and highlyaccurate driving can be performed.

Although the current control system is explained in the above-mentionedrespective embodiments, the control system may be a voltage controlsystem.

Error detection, error processing, and an operation of a control systemin the respective embodiments will be explained with reference to aflowchart in FIG. 36. In this explanation, a counter has a resetfunction.

The surface sensor 2109 measures a drive state of the belt 2106 or thedrum 2126 (S1). A value necessary for performing position control is anaccumulated count number (number) from an initial period. However, evenwhen a counter has a reset function and performs reset, position controlis possible by saving an accumulated count number in a memory.

A control unit judges whether a pulse count number measured by thecounter is within a defined range (S2). When the pulse count number iswithin the defined range, since the count number is a normal measurementvalue, the control unit additionally saves a count number measured bythe counter in addition to a count number accumulated to that point in amemory (check 1) (S3). Here, the memory (check 1) means a specificsaving area in the RAM 2138.

Thereafter, the control unit resets the counter (S4) and performsfeedback control using the value additionally saved in the memory (check1) (S5). Note that, an initial value of the memory (check 1) is 0.

If the count number measured by the counter is not within the definedrange in S2, since the count number is an abnormal measured value of ajoint or the like, the control unit additionally saves a dummypulse(more strictly, dummy pulse number) in the memory (check 1) (S6).

Thereafter, the control unit resets the counter and performs thefeedback control using the value of the dummy pulse additionally savedin the memory (check 1).

The counter is reset once per one loop, which makes it easy to obtain acount number per sampling time and also makes it possible to prevent acount number, which does not satisfy the defined range at the time ofabnormality such as a joint, from being saved.

FIG. 37 is a flowchart about a case in which a counter does not have thereset function.

The surface sensor 2109 measures a drive state of the belt 2106 or thedrum 2126 (S1). Since position control is performed here, an accumulatedpulse number from the start of drive is counted in the counter. First,the control unit saves a present count number in a memory area check 1(S2). An accumulated count number at immediately preceding sampling timeis saved in a memory area check 2. The control unit can calculate apulse number at the present sampling time by calculating a differencebetween check 1 and check 2 (S3).

Here, an initial value of check 2 is 0. Next, the control unit checkswhether the calculated pulse number at the present sampling time iswithin a defined count range (S4). If the pulse number is within thedefined count range, the control unit performs control without enteringa correction loop. At this point, a value to be used in the control iscalculated as the present counter value (check 1)+(the number of timesof correction×dummy pulse number)−dummy 1 (S5). Here, dummy 1 indicatesaccumulated and saved error counts, which are measured in the error partinadvertently. An initial value of dummy 1 is 0. In addition, an initialvalue of the number of times of correction is 0.

A value calculated by the above-mentioned method is input as a dummypulse number. After error detection, the control unit writes a value ofthe present count number check 1 over check 2 and saves the value (S6).In this way, the value can be used in the next step as an accumulatedcount number at immediately preceding sampling time. Then, the controlunit executes control.

If the pulse number at the present sampling time is not within thedefined count range in S4, the control unit judges that the pulse numberis an error and performs error processing. First, the control unitaccumulates and saves the count number, which is measured inadvertently,in dummy 1 (S7) and adds 1 to the number of times of correction (S8). Avalue to be used in the control is the same as the above expression.However, since the number of times of correction is larger by one andthe accumulated value in dummy 1 is different, the value is subjected toerror processing and input to the control loop. Thereafter, the controlunit writes a value of the present count number check 1 over check 2 andsaves the value.

In this way, the value can be used in the next step as an accumulatedcount number at immediately preceding sampling time. Then, the controlunit executes control.

Since the control loop proceeds in such a flow, even if an error ispresent, the error is detected correctly, and the error processing isperformed surely. This makes it possible to drive the belt 2106 or thedrum 2126, which is an object of drive, highly accurately.

A nineteenth embodiment of the invention will be hereinafter explainedwith reference to FIGS. 38 to 44.

First, with reference to FIG. 38, a basic structure of a belt driveapparatus including a belt serving as a rotating body to be an object ofposition control (drive control, displacement control) will beexplained. The belt in this context is an endless belt wound around atleast two shafts and is equivalent to a photosensitive belt, anintermediate transfer belt, and a direct transfer belt to be describedlater.

A drive shaft 3101 is attached to a rotation shaft of a gear 3100 to becapable of rotating synchronously with the rotation shaft. A gear 3103is attached to a rotation shaft of a motor 3102 to transmit rotation ofthe motor 3102 serving as a drive source via a gear 3103 and a gear 3100and drive to rotate the drive shaft 3101. A belt 3106, which is anobject of drive and an object of position control, is wound around thedrive shaft 3101 and driven shafts 3104 and 3105 such that a constanttension is applied to the belt 3106 by a tension roller 3107.

A linear scale 3108 serving as a scale is stuck on a surface of the belt3106 along a moving direction of the belt 3106. This linear scale 3108is read by a surface sensor 3109 consisting of a reflectivephoto-sensor, whereby a drive state (fluctuation in a position,fluctuation in velocity) of the belt 3106 is measured. The linear scale3108 and the surface sensor 3109 constitute a first signal generatingunit.

The belt 3106, which is the object of drive, is driven to rotate byrotating the motor 3102. Although the linear scale 3108 is stuck at anend on the surface of the belt 3106 here, the linear scale 3108 may bestuck in a central part or on a back of the belt 3106. In addition, ascale may be written on the belt 3106 directly.

A basic structure of a rotating body drive apparatus including arotating body to be an object of position control will be explained withreference to FIG. 39. The rotating body in this context is equivalent toa photosensitive drum and a transfer drum to be described later.

A drive pulley 3125 is attached to a rotation shaft 3124 of a gear 3122.A gear 3123 engaging with the gear 3122 is attached to a rotation shaftof a motor 3121 serving as a drive source. The drive pulley 3125 isdriven to rotate by rotation of the motor 3121.

A motor shaft encoder 3129 serving as second signal generating means isattached to the motor 3121. A timing belt 3131 is wound around the drivepulley 3125 and a driven pulley 3128 such that a constant tension isapplied to the timing belt 3131 by a tension pulley 3130. A drum 3126serving as a rotating body, which is an object of drive and an object ofposition control, is attached to the driven pulley 3128 via a shaft 3127such that coaxiality is kept. A linear scale 3108 serving as a scale isstuck on a surface of the drum 3126, which is the object of drive, alonga peripheral direction thereof. The linear scale 3108 is read by thesurface sensor 3109, whereby a drive state (fluctuation in velocity) ofthe drum 3126 is measured.

An encoder may be attached to a driven shaft that supports the belt 3106or a shaft, which rotates following the motor shaft of the drum 3126 (ina broad sense, a shaft that rotates following a rotating body), ratherthan the motor shaft.

The drum 3126 is driven to rotate by rotating the motor 3121. The linearscale 3108 is stuck to an end of the surface of the drum 3126 as well inthis structure. However, the linear scale 3108 may be stuck in a centralpart of the surface of the drum 3126 or, if the drum 3126 is tubular,may be stuck on a back thereof. In addition, a scale may be written onthe drum 3126 directly. Any object may be used instead of a scale aslong as positional displacement (drive displacement) of a rotating bodycan be grasped as some signal amount using the object.

FIG. 40 is an enlarged view of a part of the linear scale 3108 that isstuck to the belt 3106 in FIG. 38 or the drum 3126 in FIG. 39. Patterns(reference graduations for signal and pulse generation) 3108 a, whichmake it possible to measure a drive state, are written in the linearscale 3108 at equal intervals in a moving direction of the rotating bodyby a method like laser irradiation.

More specifically, the patterns 3108 a are written on a tape made ofaluminum, and light emitted from a light-emitting element to bedescribed later of the surface sensor 3109 is irradiated on the linearscale 3108 and reflected, and a light-receiving element to be describedlater of the surface sensor 3109 detects the reflected light. Since thereflected light is intense in parts where the patterns 3108 a are notwritten and the reflected light is weak in parts where the patterns 3108a are written, the patterns 3108 a of the linear scale 3108 isrecognized. Although an aluminum tape is used as a base material of thelinear scale 3108 here, a tape of other materials may be used as long asa drive state can be measured.

FIG. 41 is a block diagram of a structure of a control system thatsubjects angular displacement of the motor 3121 to digital control basedon an output signal of the motor shaft encoder 3129 in a current controlsystem common to the respective embodiments.

In FIG. 41, reference numeral 3135 denotes a microcomputer including amicroprocessor 3136, a read only memory (ROM) 3137, and a random accessmemory (RAM) 3138. The microprocessor 3136, the read only memory (ROM)3137, and the random access memory (RAM) 3138 are connected to oneanother via a bus 3143.

Reference numeral 3139 denotes an instruction generating device thatoutputs a state instruction signal for instructing angular displacementof the motor 3121. The instruction generating device 3139 generates atarget angular displacement instruction signal. An output side of theinstruction generating device 3139 is also connected to the bus 3143.Reference numeral 3142 denotes an interface device for detection thatprocesses an output pulse of the motor shaft encoder 3129 and convertsthe output pulse into a digital numerical value. The interface devicefor detection 3142 includes a counter that counts an output pulse of themotor shaft encoder 3129. The interface device for detection 3142multiplies a numerical value counted by the counter by a predeterminedconversion constant of pulse number versus angular displacement andconverts the numerical value into angular displacement of the motorshaft. A motor drive current is taken into the microcomputer 3135 from acurrent sensor 3144 via an I/O 3145.

Reference numeral 3140 denotes an interface for DC motor drive. Theinterface for DC motor drive 3140 converts a calculation result of afeedback control system, which is described in embodiments to bedescribed later, obtained by the microcomputer 3135 into a pulse-likesignal (control signal) for actuating a power semiconductor, forexample, a transistor constituting a motor (DC motor) drive device 3141according to motor shaft angular displacement and target angulardisplacement.

The DC motor drive device 3141 operates based on the pulse-like signalfrom the interface for DC motor drive 3140 and controls a voltage to beapplied to the motor 3121. As a result, the motor 3121 is controlled tofollow up predetermined angular displacement instructed by theinstruction generating device 3139. Angular displacement of the motor3121 is detected by the motor shaft encoder 3129 and the interfacedevice 3142, and taken into the microcomputer 3135, and the control isrepeated.

The linear scale 3108, the surface sensor 3109, and the microcomputer3135 serving as control means constitute a position control device thatcontrols position of a rotating body in this embodiment.

Here, angular displacement is detected directly from the motor 3121using an encoder or the like. The same holds true for a method ofdetecting drive of the belt 3106 and the drum 3126 driven by the motor3102 and the motor 3121.

In addition, although the current control system is explained, thecontrol system may be a voltage control system.

Before explaining characteristics of this embodiment, first, usual drivecontrol, which has been performed conventionally, will be explained withreference to a feedback control system shown in FIG. 42. In thisfeedback control system, a control signal is output from a controller3150, and a drive source of a plant 3151 is driven in response to thecontrol signal. Here, the controller 3150 also includes a currentcontrol loop, and the plant 3151 means an overall structure (drivedevice) that drives the belt 3106 and the drum 3126 with the motors 3102and 3121 shown in FIGS. 38 and 39.

The surface sensor 3109 measures a drive state of a rotating body suchas the belt 3106 and the drum 3126 to obtain a displacement measurementsignal value 3152. This displacement measurement signal value 3152 isfeedbacked, and a subtracter 3154 compares the fed-back displacementmeasurement signal value 3152 and a reference signal 3153 to calculate adeviation 3155 between present displacement and target displacement. Anew control signal is created by inputting this deviation 3155 to thecontroller 3150.

However, when only the usual feedback control is performed as describedabove, it is judged that driving is slow, and control cannot beperformed normally when a signal is not obtained temporarily due to atrouble of the surface sensor 3109 or the scale 3108.

In addition, when no signal is obtained at all, since a feedback signalis not obtained, the control unit takes measures to stop driving, andcontrol cannot be performed at all.

Thus, in this embodiment, to prevent the apparatus from stopping in thisway (dead time in work time from occurring), two kinds of signals,namely, a first signal obtained from the surface sensor 3109 that readsa scale pulse and a second signal obtained from the motor shaft encoder3129, are adopted as control signals. These two signals are used as afeedback signal (control signal) selectively to perform processing(switching processing) that prevents the control system from being madeunstable.

FIG. 43 shows a control system in at the time when switching processingin this embodiment is performed. A control signal is output from thecontroller 3150, and the drive source of the plant 3151 is driven by thecontrol signal. Here, the controller 3150 also includes a currentcontrol loop, and the plant 3151 means an overall structure (drivedevice) that drives the belt 3106 and the drum 3126 with the motors 3102and 3121 as shown in FIGS. 38 and 39.

The surface sensor 3109 or the motor shaft encoder 3129 measures a drivestate of the rotating body such as the belt 3106 or the drum 3126 toobtain a surface sensor measurement displacement signal value 3152 and amotor shaft encoder measurement displacement signal value 3156.

The respective displacement signal values are input to a switchingprocessing unit 3157. The switching processing unit 3157 selects one ofthe signals and outputs the signal as a feedback signal according to ameasured value or a state of the entire control system at that point.

The subtracter 3154 compares a feedback value 3158 selected by theswitching processing unit 3157 and the reference signal 3153 tocalculate the deviation 3155 between present displacement and targetdisplacement. A new control signal is created by inputting thisdeviation 3155 to the controller 3150. This is the control system at thetime when the switching processing is performed.

In the control system in FIG. 43, the entire control system excludingthe plant 3151 constitutes the control unit (microcomputer 3135) in thisembodiment.

This embodiment is characterized in that, when control is performedbased on the second signal (signal from the motor shaft encoder 3129),in switching the control to control based on the first signal (scalepulse from the surface sensor 3109) at arbitrary time, the control basedon the second signal is continued if the first signal cannot be read.

This control method (algorithm) will be explained with reference to aflowchart in FIG. 44.

At present, the belt 3106 or the drum 3126 is driven based on a signalfrom the motor shaft encoder 3129 (S1). At arbitrary time, when it isintended to change a feedback signal from a signal from the motor shaftencoder 3129 to a signal from the surface sensor 3109, first, thecontrol unit judges whether abnormality is present in the surface sensor3109 (S2).

As criteria for this judgment, for example, a signal notifyingabnormality is sent from the surface sensor 3109, a normal signal is notsent from the surface sensor 3109, or a measurement displacement signalto be feedbacked is not received in an arbitrary time section or isabnormal.

Reasons for occurrence of the abnormality include decline in measurementfunction of the surface sensor 3109 itself and deterioration in time ofthe scale 3109.

If there is no abnormality and no problem in the surface sensor 3109,the control unit selects the surface sensor signal (first signal) as afeedback signal to drive the belt 3106 or the drum 3126 based on thefirst signal (S3).

If abnormality is present in the surface sensor 3109, the control unitselects the signal from the motor shaft encoder 3129 instead of thesurface sensor signal as a feedback signal to drive the belt 3106 or thedrum 3126 (S4).

Instead of the signal from the motor shaft encoder 3129, a motor fgsignal for measuring a drive state of a motor using a Hall element maybe adopted as the second signal. A motor mr signal for measuring a drivestate of motor using a magnetic resistance effect element (MR element)may be adopted as the second signal. This makes it possible to reduce aspace required by the motor shaft encoder 3129 and to reduce apparatuscost on the drive source side. Moreover, a method of attaching anencoder to a drive shaft of the belt 3106 or the drum 3126, a drivenshaft (supporting shaft) of the belt 3106, or the like rather than themotor shaft may be used.

A control signal is selected to perform control in this way, whereby itbecomes possible to perform control without making driving of the belt3106 or the drum 3126 driven by the signal from the motor shaft encoder3129 unstable and without stopping the apparatus.

A twentieth embodiment of the invention will be explained with referenceto FIG. 45. Note that, a structure and a functions according to thetwentieth embodiment are identical with those according to theabove-mentioned embodiments, an explanation of the structure and thefunctions will be omitted, and only a principal part (control method)will be explained (the same holds true for other embodiments).

This embodiment is characterized in that, in driving of the belt 3106 orthe drum 3126, when switching from the motor shaft encoder signal(second signal) to the surface sensor signal (first signal) is possible,a difference between displacement calculated from a surface sensorsignal to be used after the switching and target displacement iscorrected.

At present, the belt 3106 or the drum 3126 is driven according to asignal from the motor shaft encoder 3129 (S11). At arbitrary time, whenit is intended to change a feedback signal from a signal from the motorshaft encoder 3129 to a surface sensor signal, first, the control unitjudges whether abnormality is present in the surface sensor 3109 (S12).

If there is no abnormality and no problem in the surface sensor 3109,the control unit selects the surface sensor signal as the feedbacksignal to drive the belt 3106 or the drum 3126 (S13). In that case, onlywhen the surface sensor signal is selected for the first time, thecontrol unit calculates a difference between displacement calculatedfrom the surface sensor signal and target displacement and saves thedifference in a memory (e.g., RAM 3138) to perform correction processing(S14).

If abnormality is present in the surface sensor 3109 in S12, the controlunit selects the motor shaft encoder signal instead of the surfacesensor signal as the feedback signal to drive the belt 3106 or the drum3126 (S15).

Such control makes it possible to, when the belt 3106 or the drum 3126is driven according to a signal from the motor shaft encoder 3129 andwhen it is attempted to switch control to control according to thesurface sensor signal at arbitrary time, continue to drive the belt 3106or the drum 3126 without causing sudden suspension of the apparatus oradversely affecting the entire system and continue to control thedriving of the belt 3106 or the drum 3126 correctly according to withthe target displacement.

A twenty-first embodiment of the invention will be explained withreference to FIG. 46.

This embodiment is characterized in that, when switching from a motorshaft encoder signal to a surface sensor signal is possible, adifference between displacement calculated from the surface sensorsignal and displacement calculated from the motor shaft encoder signalis corrected.

At present, the belt 3106 or the drum 3126 is driven according to asignal from the motor shaft encoder 3129 (S21). At arbitrary time, whenit is intended to change a feedback signal from a motor shaft encodersignal to a surface sensor signal, first, the control unit judgeswhether abnormality is present in the surface sensor 3109 (S22).

If there is no abnormality and no problem in the surface sensor 3109,the control unit selects the surface sensor signal as the feedbacksignal to drive the belt 3106 or the drum 3126 (S23). In that case, onlywhen the surface sensor signal is selected for the first time, thecontrol unit calculates a difference between displacement (position)calculated from the surface sensor signal (a control signal to be usedafter switching) and displacement calculated from the motor shaftencoder signal (control signal used before the switching) and saves thedifference to perform correction processing (S24).

If abnormality is present in the surface sensor 3109 in S22, the controlunit selects the motor shaft encoder signal instead of the surfacesensor signal as the feedback signal to drive the belt 3106 or the drum3126 (S25).

Such control makes it possible to, when the belt 3106 or the drum 3126is driven according to a signal from the motor shaft encoder 3129 andwhen it is attempted to switch control to control according to thesurface sensor signal at arbitrary time, continue to drive the belt 3106or the drum 3126 without causing sudden suspension of the apparatus oradversely affecting the entire system, continue to control the drivingof the belt 3106 or the drum 3126 correctly according to the targetdisplacement, and shift from control according to the motor shaftencoder signal to control according to the surface sensor signalcontinuously.

A twenty-second embodiment of the invention will be explained withreference to FIG. 47.

This embodiment is characterized in that control is performed accordingto a measurement signal (simply referred to as a signal as well) fromthe motor shaft encoder 3129 from the time when driving of the belt 3106or the drum 3126 is started until the time when the driving reaches asteady state and, after the driving reaches the steady state, thecontrol is switched to control according to a measurement signal (simplyreferred to as a signal as well) from the surface sensor 3109 to drivethe belt 3106 or the drum 3126.

When the signal from the surface sensor 3109 is used from the time whenthe driving of the belt 3106 or the drum 3126 is started until thedriving reaches the steady state, a control system is made unstable ifthere is a part where a signal is not obtained due to a joint of ascale, and driving cannot be started surely. Therefore, a method ofusing measuring means other than the surface sensor 3109 is effective toobtain stable starting drive.

Drive control for the belt 3106 or the drum 3126 according to the motorshaft encoder signal is started. After the driving is started, thecontrol unit judges whether the driving of the belt 3106 or the drum3126 has reached the steady state (S31).

In this case, the control unit may determine whether the driving hasreached the steady state based on an output from the motor shaft encoder3129, which measures a drive state of the belt 3106 or the drum 3126, ormay determine whether the driving has reached the steady state based onan output from the surface sensor 3109. In addition, when the driving isconsidered to be in the steady state if certain time has elapsed fromthe start of driving rather than on the basis of a measurement result,the control unit may determine whether the driving has reached thesteady state according to time.

The control unit continues the control according to the motor shaftencoder signal until the driving of the belt 3106 or the drum 3126reaches the steady state (S32). When the driving of the belt 3106 or thedrum 3126 has reached the steady state, the control unit switches thefeedback signal from the motor shaft encoder signal to the surfacesensor signal to drive the belt 3106 or the drum 3126 according to thesurface sensor signal after that (S33).

A twenty-third embodiment of the invention will be explained withreference to FIG. 48.

This embodiment is characterized in that, when a feedback signal isswitched from a motor shaft encoder signal to a surface sensor signalafter driving of the belt 3106 or the drum 3126 has reached a steadystate, a difference between displacement calculated from the surfacesensor signal and target displacement is corrected.

Drive control for the belt 3106 or the drum 3126 according to the motorshaft encoder signal is started. After the driving is started, thecontrol unit judges whether the driving of the belt 3106 or the drum3126 has reached the steady state (S41).

The control unit continues control according to the motor shaft encodersignal until the driving of the belt 3106 or the drum 3126 reaches thesteady state (S42). At the same time, the control unit measuresdisplacement of the belt 3106 or the drum 3126 using the surface sensorsignal and saves a difference between the displacement and targetdisplacement (S43). This difference value is always updated while thecontrol according to the motor shaft encoder signal is continued.

When the driving of the belt 3106 or the drum 3126 has reached thesteady state, the control unit switches the feedback signal from themotor shaft encoder signal to the surface sensor signal (S44) and, atthat point, performs correction processing using the difference valuesaved in S43 to perform surface sensor control (S45). Thereafter, thebelt 3106 or the drum 3126 is driven according to the surface sensorsignal, and the difference value is not updated.

Such control makes it possible to eliminate influence of a surfacesensor signal value until the driving reaches the steady state(instability of the control) and control the driving of the belt 3106 orthe drum 3126 correctly according to the target displacement.

A twenty-fourth embodiment of the invention will be explained withreference to FIG. 49.

This embodiment is characterized in that, when a feedback signal isswitched from a motor shaft encoder signal to a surface sensor signalafter driving of the belt 3106 or the drum 3126 has reached a steadystate, a difference between displacement calculated from the surfacesensor signal and displacement calculated from the motor shaft encodersignal is corrected.

Drive control for the belt 3106 or the drum 3126 according to the motorshaft encoder signal is started. After the driving is started, thecontrol unit judges whether the driving of the belt 3106 or the drum3126 has reached the steady state (S51). The control unit continuescontrol according to the motor shaft encoder signal until the driving ofthe belt 3106 or the drum 3126 reaches the steady state (S52).

At the same time, the control unit measures displacement of the belt3106 or the drum 3126 using the surface sensor signal and saves adifference between the displacement and displacement calculated from themotor shaft encoder signal (S53). This difference value is alwaysupdated while the control according to the motor shaft encoder signal iscontinued.

When the driving of the belt 3106 or the drum 3126 has reached thesteady state, the control unit switches the feedback signal from themotor shaft encoder signal to the surface sensor signal (S54) and, atthat point, performs correction processing using the difference valuesaved in S53 (S55) to perform control according to the surface sensorsignal. Thereafter, the belt 3106 or the drum 3126 is driven accordingto the surface sensor signal, and the difference value is not updated.

Such control makes it possible to eliminate influence of a surfacesensor signal value until the driving reaches the steady state and, inthe driving of the belt 3106 or the drum 3126, control the drivingcontinuously according to the displacement calculated from the motorshaft encoder signal that has been used as the feedback signal.

In this embodiment, the motor shaft encoder signal may be a motor fgsignal or a motor mr signal as in the above-mentioned embodiments.

A twenty-fifth embodiment of the invention will be explained withreference to FIG. 50.

This embodiment is characterized in that, when some abnormality occursin the surface scale 3108 or the surface sensor 3109 and a measurementsignal is not obtained while the belt 3106 or the drum 3126 is subjectedto drive control according a measurement signal from the surface sensor3109, the control is switched to control according to a measurementsignal from the motor shaft encoder 3129.

Drive control for the belt 3106 or the drum 3126 according to a surfacesensor signal is continued. The control unit judges whether an outputfrom the surface sensor 3109 is normal while continuing the drivecontrol (S61).

As criteria for this judgment, for example, a signal notifyingabnormality is sent from the surface sensor 3109, a normal signal is notsent from the surface sensor 3109, or a measurement displacement signalto be feedbacked is not received in an arbitrary time section or isabnormal.

If there is no abnormality in the output from the surface sensor 3109and there is no problem, the control unit continues to select thesurface sensor signal as the feedback signal (S62) to drive the belt3106 or the drum 3126.

If there is abnormality in the surface sensor 3109 in S61, the controlunit selects the motor shaft encoder signal rather than the surfacesensor signal as the feedback signal (S63) to drive the belt 3106 or thedrum 3126.

A twenty-sixth embodiment of the invention will be explained withreference to FIG. 51.

This embodiment is characterized in that, when a feedback signal isswitched from a surface sensor signal to a motor shaft encoder signal indriving of the belt 3106 or the drum 3126, a difference betweendisplacement calculated from the motor shaft encoder signal and targetdisplacement is corrected.

Drive control for the belt 3106 or the drum 3126 according to thesurface sensor signal is continued. The control unit judges whether anoutput from the surface sensor 3109 is normal while continuing the drivecontrol (S71). If there is no abnormality in the output from the surfacesensor 3109 and there is no problem, the control unit continues toselect the surface sensor signal as the feedback signal (S72) to drivethe belt 3106 or the drum 3126.

At the same time, the control unit measures displacement of the belt3106 or the drum 3126 using the motor shaft encoder signal and saves adifference between the displacement and target displacement (S73). Thisdifference value is always updated while the control according to thesurface sensor signal is continued.

If there is abnormality in the surface sensor 3109 in S71, the controlunit switches the feedback signal from the surface sensor signal to themotor shaft encoder signal (S74) and, at that point, performs correctionprocessing using the difference value saved in S73 to perform controlaccording to the motor shaft encoder signal (S75). Thereafter, the belt3106 or the drum 3126 is driven according to the motor shaft encodersignal, and the difference value is not updated.

Such control makes it possible to, even if abnormality occurs in surfacesensor measurement (including both abnormality of the surface sensor3109 itself and abnormality of the scale 3108), continue the driving ofthe belt 3106 or the drum 3126 and control the belt 3106 and the drum3126 correctly according to the target displacement without causingsudden suspension of the apparatus or adversely affecting the entiresystem.

A twenty-seventh embodiment of the invention will be explained withreference to FIG. 52.

This embodiment is characterized in that, when a feedback signal isswitched from a surface sensor signal to a motor shaft encoder signal indriving of the belt 3106 or the drum 3126, a difference betweendisplacement calculated from the motor shaft encoder signal anddisplacement calculated from the surface sensor signal is corrected.

Drive control for the belt 3106 or the drum 3126 according to thesurface sensor signal is continued. The control unit judges whether anoutput from the surface sensor 3109 is normal while continuing the drivecontrol (S81). If there is no abnormality in the output from the surfacesensor 3109 and there is no problem, the control unit continues toselect the surface sensor signal as the feedback signal (S82) to drivethe belt 3106 or the drum 3126.

At the same time, the control unit measures displacement of the belt3106 or the drum 3126 using the motor shaft encoder signal and saves adifference between the displacement and target displacement (S83). Thisdifference value is always updated while the control according to thesurface sensor signal is continued.

If there is abnormality in the surface sensor 3109 in S81, the controlunit switches the feedback signal from the surface sensor signal to themotor shaft encoder signal (S84) and, at that point, performs correctionprocessing using the difference value saved in S83 (S85) to performcontrol according to the motor shaft encoder signal. Thereafter, thebelt 3106 or the drum 3126 is driven according to the motor shaftencoder signal, and the difference value is not updated.

Such control makes it possible to, even if abnormality occurs in surfacesensor measurement, continue the driving of the belt 3106 or the drum3126 and shift to the control according to the motor shaft encodersignal continuously from the control according to the surface signal.

In this embodiment, again, the motor shaft encoder signal may be a motorfg signal or a motor mr signal.

A twenty-eighth embodiment of the invention will be explained withreference to FIG. 53.

This embodiment is characterized in that, in a state in which someabnormality occurs in the surface scale 3108 or the surface sensor 3109and a measurement signal is not obtained, and while driving of the belt3106 or the drum 3126 is performed using a measurement signal of themotor shaft encoder 3129, when the abnormality in the surface scale 3108or the surface sensor 3109 is eliminated and the measurement signal isobtained, control is switched to control according to a measurementsignal from the surface sensor 3109 to drive the belt 3106 or the drum3126.

Abnormality (decline or incapability in a measurement function) occursin the surface sensor 3109, and drive control for the belt 3106 or thedrum 3126 according to a motor encoder signal is continued (S91). Thecontrol unit checks a state of the surface sensor 3109 while continuingthe drive control (S92).

As criteria for this judgment, for example, a signal notifyingabnormality is not sent from the surface sensor 3109, a signal is sentfrom the surface sensor 3109 normally, or a measurement displacementsignal to be feedbacked is received in an arbitrary time section or isnormal.

When it is judged that there is no abnormality in the state of thesurface sensor 3109 and the surface sensor 3109 is normal, the controlunit selects a surface sensor signal instead of the motor shaft encodersignal as the feedback signal (S93) to drive the belt 3106 or the drum3126.

When the measurement function of the surface sensor 3109 does not revivein S92, the control unit continues the control according to the motorshaft encoder signal (S94).

A twenty-ninth embodiment of the invention will be explained withreference to FIG. 54.

This embodiment is characterized in that, when a feedback signal isswitched from a motor shaft encoder signal to a surface sensor signal indriving of the belt 3106 or the drum 3126, a difference betweendisplacement calculated from the surface sensor signal and targetdisplacement is corrected.

Abnormality occurs in the surface sensor 3109, and drive control for thebelt 3106 or the drum 3126 according to the motor encoder signal iscontinued (S101). The control unit checks a state of the surface sensor3109 while continuing the drive control (S102). When it is judged thatthere is no abnormality in the state of the surface sensor 3109 and thesurface sensor 3109 is normal, the control unit selects the surfacesensor signal as the feedback signal (S103) to drive the belt 3106 orthe drum 3126.

In that case, only when the surface sensor signal is selected for thefirst time, the control unit calculates a difference between thedisplacement calculated from the surface sensor signal and the targetdisplacement and saves the difference to perform correction processing(S104). Thereafter, the control unit continues only the correctionprocessing without updating this difference. The belt 3106 or the drum3126 is driven according to the surface sensor signal.

When a measurement function of the surface sensor 3109 does not revivein S102, the control unit continues the control according to the motorshaft encoder signal (S105).

Such control makes it possible to, in the driving of the belt 3106 orthe drum 3126 in which abnormality occurs in surface sensor measurement,if the surface sensor measurement returns to normal, continue thedriving of the belt 3106 or the drum 3126 and continuously control thedriving of the belt 3106 or the drum 3126 according to the targetdisplacement correctly without causing sudden suspension of theapparatus or adversely affecting the entire system.

A thirtieth embodiment of the invention will be explained with referenceto FIG. 55.

This embodiment is characterized in that, when a feedback signal isswitched from a motor shaft encoder signal to a surface sensor signal indriving of the belt 3106 or the drum 3126, a difference betweendisplacement calculated from the surface sensor signal and displacementcalculated from the motor shaft encoder signal is corrected.

Abnormality occurs in the surface sensor 3109, and drive control for thebelt 3106 or the drum 3126 according to the motor encoder signal iscontinued (S111). The control unit checks a state of the surface sensor3109 while continuing the drive control (S112). When it is judged thatthere is no abnormality in the state of the surface sensor 3109 and thesurface sensor 3109 is normal, the control unit selects the surfacesensor signal as the feedback signal (S113) to drive the belt 3106 orthe drum 3126.

In that case, only when the surface sensor signal is selected for thefirst time, the control unit calculates a difference between thedisplacement calculated from the surface sensor signal and thedisplacement calculated from the motor shaft encoder signal and savesthe difference to perform correction processing (S114). Thereafter, thecontrol unit continues only the correction processing without updatingthis difference. The belt 3106 or the drum 3126 is driven according tothe surface sensor signal.

When a measurement function of the surface sensor 3109 does not revivein S112, the control unit continues the control according to the motorshaft encoder signal (S115).

Such control makes it possible to, in the driving of the belt 3106 orthe drum 3126 in which abnormality occurs in surface sensor measurement,if the surface sensor measurement returns to normal, continue thedriving of the belt 3106 or the drum 3126 and shift to the controlaccording to the surface signal continuously from the control accordingto the motor shaft encoder signal.

In this embodiment, again, the motor shaft encoder signal may be a motorfg signal or a motor mr signal.

In the twenty-eighth embodiment, the “state in which abnormality occursin the surface sensor 3109 and drive control for the belt 3106 or thedrum 3126 according to a motor shaft encoder signal is continued” is theend state in the twenty-fifth embodiment, and the start in FIG. 53 isthe end in FIG. 50. Similarly, the start in FIG. 54 (the twenty-ninthembodiment) is the end in FIG. 51 (the twenty-sixth embodiment), and thestart in FIG. 55 (the thirtieth embodiment) is the end in FIG. 52 (thetwenty-seventh embodiment).

A thirty-first embodiment of the invention will be explained withreference to FIGS. 56 and 57.

This embodiment is characterized in that drive control for the belt 3106or the drum 3126 is performed according to a measurement signal from thesurface sensor 3109, when a joint is present in the surface scale 3108,a measurement signal from the motor shaft encoder 3129 is used when ameasurement position of the surface sensor 3109 enters the joint, andthe control is switched to the control according to the measurementsignal from the surface sensor 3109 if the measurement position returnsto a usual position from the joint to drive the belt 3106 or the drum3126.

FIG. 56 is an enlarged view of a joint part of the linear scale 3108stuck on the belt 3106 in FIG. 38 or the drum 3126 in FIG. 39.

There are two kinds of joints in a method of sticking a tape-like scalesuch as the linear scale 2108. One is a physical joint 3132 where thelinear scale 3108 is not physically continuous as shown in FIG. 56A. Theother is a writing joint 3133 as a blank part, where nothing is writtenon the linear scale 3108 because of a problem of accuracy or the like atthe time when the patterns 3108 a are written, although the linear scale3108 is present continuously as shown in FIG. 56B.

There is no tape at all in the physical joint 3132, and only a tapewithout the patterns 3108 a is present in the writing joint 3133. Thus,a usual measurement signal is not obtained in both the joints.Therefore, in this embodiment, these joints are treated as the samejoints and will be hereinafter expressed simply as “joint”. In thisexplanation, it is assumed that the physical joint 3123 and the writingjoint 3133 are present separately. However, the physical joint 3123 andthe writing joint 3133 may be treated as joints even if the physicaljoint 3123 and the writing joint 3133 are mixed. In addition, a usualmeasurement signal is not obtained due to an output error of the surfacesensor 3109 itself including scratches, stains, and noise as in thejoints.

A control operation in this embodiment will be explained with referenceto a flowchart in FIG. 57.

The drive control for the belt 3106 or the drum 3126 according to asurface sensor signal is continued. The control unit judges whether thesurface sensor 3109 is in the joint part while continuing the drivecontrol (S121).

As criteria for this judgment, for example, a signal notifying that thesurface sensor 3109 is in the joint is sent from the surface sensor3109, or a normal signal is not sent from the surface sensor 3109. Ifthe surface sensor 3109 is not in the joint, the control unit continuesto select the surface sensor signal as the feedback signal (S122) todrive the belt 3106 or the drum 3126.

If it is judged in S121 that the surface sensor 3109 is in the joint,the control unit selects the motor shaft encoder signal instead of thesurface sensor signal as the feedback signal (S123) to drive the belt3106 or the drum 3126.

After the surface sensor 3109 entered the joint, when it is judged thatthe surface sensor 3109 has exited the joint, the control unit selectsthe surface sensor signal as the feedback signal to drive the belt 3106or the drum 3126.

A thirty-second embodiment will be explained with reference to FIG. 58.

This embodiment is characterized in that, in driving of the belt 3106 orthe drum 3126, when a feedback signal is switched from a surface sensorsignal to a motor shaft encoder signal, a difference betweendisplacement calculated from the motor shaft encoder signal and targetdisplacement is corrected, or when the feedback signal is switched fromthe motor shaft encoder signal to the surface sensor signal, adifference between displacement calculated from the surface sensorsignal and the target displacement is corrected.

Drive control for the belt 3106 or the drum 3126 according to thesurface sensor signal is continued. The control unit judges whether thesurface sensor 3109 is in the joint part while continuing the drivecontrol (S131). If the surface sensor 3109 is not in the joint, thecontrol unit continues to select the surface sensor signal as thefeedback signal (S132). At this point, the control unit saves adifference a between the displacement calculated from the motor shaftencoder signal and the target displacement (S133).

This difference value is updated while the surface sensor 3109 is not inthe joint and the surface sensor control is continued. Then, the controlunit performs correction processing using a difference b betweendisplacement calculated from a surface sensor signal, which wasgenerated in response to the surface sensor 3109 entering and exitingthe joint before, and the target displacement (S134) to drive the belt3106 or the drum 3126.

When it is judged in S131 that the surface sensor 3109 is in the joint,the control unit selects the motor shaft encoder signal instead of thesurface sensor signal as the feedback signal (S135). At this point, thecontrol unit saves the difference between the displacement calculatedfrom the surface sensor signal and the target displacement (S136). Thisdifference value is always updated while the surface sensor 3109 is inthe joint.

Then, the control unit performs correction processing using thedifference a between the displacement calculated from the motor shaftencoder signal, which was generated in response to the surface sensor3109 entering and exiting the joint before, and the target displacement(S137) to drive the belt 3106 or the drum 3126.

Such control makes it possible to, even if a joint is present in thescale 3108 of the belt 3106 or the drum 3126, continue driving of thebelt 3106 or the drum 3126 and control the belt 3106 or the drum 3126according to the target displacement without causing sudden suspensionof the apparatus or adversely affecting the entire system.

A thirty-third embodiment of the invention will be explained withreference to FIG. 59.

This embodiment is characterized in that, in driving of the belt 3106 orthe drum 3126, when a feedback signal is switched from a surface sensorsignal to a motor shaft encoder signal, a difference betweendisplacement calculated from the motor shaft encoder signal anddisplacement calculated from the surface sensor signal is corrected.

Drive control for the belt 3106 or the drum 3126 according to thesurface sensor signal is continued. The control unit judges whether thesurface sensor 3109 is in the joint part while continuing the drivecontrol (S141). If the surface sensor 3109 is not in the joint, thecontrol unit continues to select the surface sensor signal as thefeedback signal (S142). At this point, only when the surface sensorsignal is selected for the first time, the control unit saves adifference c between the displacement calculated from the motor shaftencoder signal and the displacement calculated from the surface sensorsignal (S143).

Then, the control unit applies correction processing to the surfacesensor signal using the calculated difference c (S144) to drive the belt3106 or the drum 3126.

When it is judged in S141 that the surface sensor 3109 is in the joint,the control unit selects the motor shaft encoder signal instead of thesurface sensor signal as the feedback signal (S145). At this point, onlywhen the motor shaft encoder signal is selected for the first time, thecontrol unit saves a difference d between the displacement calculatedfrom the motor shaft encoder signal and the displacement calculated fromthe surface sensor signal (S146). Then, the control unit appliescorrection processing to the motor shaft encoder signal using thecalculated difference d (S147) to drive the belt 3106 or the drum 3126.

Such control makes it possible to, even if a joint is present in thescale 3108 of the belt 3106 or the drum 3126, continue driving of thebelt 3106 or the drum 3126 and shift from control according to thesurface control signal to control according to the motor shaft controlsignal continuously without causing sudden suspension of the apparatusor adversely affecting the entire system.

In this embodiment, again, the motor shaft encoder signal may be a motorfg signal or a motor mr signal.

When dust or sensor abnormality is avoided temporarily other than thejoint, it can be considered that the same algorithm as above is usedexcept that a part of the algorithm for judging whether a joint ispresent is changed.

Here, a state of a sensor (surface sensor 3109) at the time whenabnormality occurs in the sensor in reading a scale pulse on the belt3106 or the drum 3126 will be described.

FIG. 60 is an enlarged view of the parts of the surface sensor 3109 andthe scale 3108. The scale 3108 is stuck on the surface of the belt 3106or the drum 3126. Patterns 3108 a and patterns 3108 b are alternatelywritten on the scale 3108 at fixed intervals. Reflectance of light ishigh in the patterns 3108 b, and reflectance is low in the parts of thepatterns 3108 a compared with the patterns 3108 b.

The surface sensor 3109, which reads the patterns 3108 a and thepatterns 3108 b, are provided near the scale 3108. Light is emitted froma light-emitting section 3109 a of the surface sensor 3109. The emittedlight is irradiated on the scale 3108, and a light-receiving section3109 b receives a reflected wave of the light. Since the reflectance isdifferent in the patterns 3108 a and the patterns 3108 b, it is possibleto measure a drive state of the belt 3106 or the drum 3126 by reading adifference of intensity of light to be received.

FIG. 61 shows an output of the surface sensor 3109 at the time whenpatterns with different degrees of reflectance shown in FIG. 60 areread. A horizontal axis indicates time, and a vertical axis indicatesintensity of light to be received on the surface sensor 3109. Since thelight is intense when the patterns 3108 b are read and is weak when thepatterns 3108 a are read, an output 3170 of a sine wave shape isobtained.

This output 3170 may be used directly as a measurement signal. When itis desired to change a measurement signal to a pulse signal, anarbitrary threshold level 3171 is provided with respect to the output3170. When the output 3170 exceeds this threshold level 3171, an Hsignal is used, and when the output 3170 falls below the threshold level3171, an L signal is used, whereby the output 3170 can be obtained as arectangular pulse 3172 as shown in FIG. 62.

FIG. 63 shows a method of determination for judging whether abnormalityhas occurred in the surface sensor 3109. An upper limit level 3173 and alower limit level 3174 are provided with respect to the output 3170obtained from the surface sensor 3109. If the output 3170 is between theupper limit and the lower limit, it is judged that the output 3170 isnormal.

When abnormality occurs in the surface sensor 3109, and an output levelof the surface sensor 3109 increases to a level 3175, since the outputexceeds the upper limit level 3173, it is judged that abnormality hasoccurred. When the output level decreases to a level 3176, since theoutput falls below the lower limit level 3174, it is judged thatabnormality has occurred.

In this way, it is judged whether the surfaced sensor 3109 is abnormalor normal. Thus, if abnormality occurs, it is possible to notify thecontrol side of the occurrence of abnormality by outputting anabnormality occurrence signal from the surface sensor 3109 side.

Occurrence of abnormality may be judged by measuring time of a pulseinterval or a pulse width of the rectangular pulse 3172 shown in FIG. 62to judge whether the time of the pulse interval or the pulse width islonger or shorter than usual time.

FIG. 64 shows a method of detecting that surface sensor measurement isabnormal on the control side (control unit side) without depending onthe surface sensor 3109.

A case in which a pulse number of the rectangular pulse 3172 as shown inFIG. 62 is counted in control every sampling time to perform positioncontrol according to an accumulated count number will be considered. Ahorizontal axis indicates elapsed time per sampling time, and a verticalaxis indicates a count number (pulse count number) per sampling time.

When the position control is performed, the pulse count numberfluctuates within a fluctuation range a1 of a count number, which ispossible in usual load variation (disturbance), pulse count numbers3177, 3178, and 3179 are measured. At this point, if abnormality occursin the surface sensor 3109, since a sensor itself does not operatecorrectly, pulse count numbers 3180 and 3181 within a range a2 lowerthan usual fluctuation range a1 are measured. Alternatively, a pulsenumber 3182 within a range a3 exceeding the usual fluctuation range a1is measured.

When a pulse count number not within the usual fluctuation range a1 ismeasured, the control side judges that abnormality occurs in the surfacesensor 3109 and outputs an abnormality occurrence signal. This makes itpossible to judge or inform that surface sensor measurement isimpossible.

Next, a thirty-fourth embodiment will be explained. In the thirty-fourthembodiment, an example of performing feedback control using aninexpensive mark sensor with low resolution is described. When the marksensor with low resolution is used, there is a limit in a mark intervalthat can be detected with the resolution. More specifically, forexample, when a mark is directly provided on a surface of a drivecontrol object member moving endlessly at velocity of 282 millimetersper second, a limit of the mark interval is about 4160 micrometers. Inthis case, a position of the drive control object member can only begrasped by a unit of 4169 micrometers. Therefore, for example, whenmarks are detected in a number larger than a target mark number by one,even when a position of the drive control object member actually hasmoved further than a target position only by 1 micrometer, it is judgedthat the position of the drive control object member has moved furtherthan the target position by 4160 micrometers. Consequently, when themark sensor with low resolution is used, accuracy of causing theposition of the drive control object member to follow the targetposition is low compared with a mark sensor with high resolution.

Even an apparatus using such a mark sensor with low resolution canperform stable feedback control concerning a period of a discontinuouspart.

However, the apparatus simulatively feedbacks a mark detection signal orthe like (dummy signal) in a continuous part in the past as a markdetection signal in the discontinuous part throughout the period of thediscontinuous part. Thus, when the mark sensor with low resolution isused, an actual position in the drive control object member cannot begrasped for the period of the discontinuous part. Moreover, velocity ofthe drive control object member varies due to various errors in a drivesystem. Therefore, it is impossible to grasp to which degree an actualendless movement position immediately after the end of the period of thediscontinuous part is behind or ahead of the target position.

FIG. 65 is a graph schematically showing a position of the drive controlobject member, which is grasped based on a mark detection signal fromthe mark sensor before and after the period of the discontinuous part,to explain the position. In this graph, a horizontal axis indicates timeand a vertical axis indicates a position of the drive control objectmember with respect to the target position (a relative position).

As shown in the figure, in a period A of a continuous part, feedbackcontrol following the target position is performed based on a markdetection signal from the mark sensor. Even in this example in which themark sensor with low resolution is used, a position of the drive controlobject member in this period A can be placed within a range of about4160 micrometers around the target position by the feedback control. Onthe other hand, in a period B of a discontinuous part, the feedbackcontrol is performed using the dummy signal as described above. In thisperiod B, a position of the drive control object member cannot begrasped as described above. Here, it is assumed that a position of thedrive control object member with respect to the target position (arelative position) does not change during the period B. On the otherhand, when the period B of the discontinuous part ends, the feedbackcontrol is performed again based on a mark detection signal from themark sensor. In this case, a result of the feedback control is notinstantly reflected on change of a position of the drive control objectmember due to influence of a torque or the like applied to the drivesystem. Therefore, immediately after the period B of the discontinuouspart ends, a position of the drive control object member may deviatelargely from the target position.

FIG. 66 is a schematic diagram of a structure of a belt drive apparatusthat is a rotating body drive apparatus including a belt 4106 serving asa drive control object member. This belt 4106 is an endless belt woundaround at least two shafts and is equivalent to a photosensitive belt,an intermediate transfer belt, and a direct transfer belt.

A drive roller 4101 is fixed to a rotation shaft of a gear 4100, and agear 4103 is fixed to a rotation shaft of a motor 4102 serving as a DCmotor. When the motor 4102 serving as a drive source is driven torotate, a torque of the motor 4102 is transmitted to a drive roller 4101via the gear 4103 and the gear 4100, and the drive roller 4101 is drivento rotate. A belt 4106 is wound around the drive roller 4101 and drivenroller 4104 and 4105 such that a constant tension is applied to the belt4106 by a tension roller 4107. A linear scale, on which plural marks areformed, is stuck on a surface of the belt 4106 along a surface movingdirection (endless moving direction) of the belt 4106. In addition, asurface sensor 4109 including a reflective photo-sensor serving as markdetecting means is provided to be opposed to the linear scale 4108. Asurface moving position, which is an endless moving position, andsurface moving velocity, which is endless moving velocity, of the belt4106 are measured by reading the marks on the linear scale 4108 with thesurface sensor 4109.

FIG. 67 is a schematic diagram of a structure of a drum drive apparatusserving as a rotating body drive apparatus including a drum 4126 servingas a drive control object member. The drum 4126 is equivalent to aphotosensitive drum and a transfer drum to be described later.

A drive pulley 4125 is fixed to a rotation shaft 4124 of the gear 4122,and a gear 4123 engaging with the gear 4122 is fixed to a rotation shaftof a motor 4121 that is a DC motor serving as a drive source. When themotor 4121 is driven to rotate, a torque of the motor 4121 istransmitted to the drive pulley 4125 via the gears 4122 and 4123, andthe drive pulley 4125 is driven to rotate. A timing belt 4131 is woundaround the drive pulley 4125 and a driven pulley 4128 such that aconstant tension is applied to the timing belt 4131 by a tension pulley4130. A drum 4126 is attached to the driven pulley 4128 via a shaft 4127such that coaxiality is kept. The linear scale 4108, which is the sameas the linear scale shown in FIG. 66, is stuck on a surface of the drum4126 along a peripheral direction of the drum 4126. In addition, thesurface sensor 4109 including a reflective photo-sensor is provided as amark detecting unit to be opposed to the linear scale 4108. A surfacemoving position, which is an endless moving position, and surface movingvelocity, which is endless moving velocity, of the belt 4106 aremeasured by reading the marks on the linear scale 4108 with the surfacesensor 4109.

Note that, although the linear scale 4108 is stuck at one end of thesurface of the belt 4106 or the drum 4126 in the thirty-fourthembodiment, the linear scale 4108 may be stuck in a central part of thesurface or on a back the belt 4106 or the drum 4126. In addition, in thethirty-fourth embodiment, the marks are directly provided on a belt 4106or the drum 4126, which are a drive control object member. However, themarks may be provided on an endless moving member like the drive roller4101 or the driven roller 4104 or 4105, which moves endlessly followingthe surface movement of the belt 4106 or the driven pulley 4128, whichmoves endlessly following the surface movement of the drum 4126. Inaddition, in the thirty-fourth embodiment, the marks are provided on thebelt 4106 by sticking the linear scale 4108, on which the marks areformed in advance to continue at predetermined intervals, on the belt4106. However, the marks may be provided by directing writing the markson the belt 4106.

FIG. 68A is an enlarged view of a joint part of the linear scale 4108stuck on the belt 4106 in FIG. 66 or the drum 4126 in FIG. 67. Pluralmarks 4108 a are written in the linear scale 4108 by a method like laserirradiation at equal intervals in a surface movement direction of thebelt 4106 or the drum 4126 (hereinafter referred to as “rotating body”according to circumstances). More specifically, the marks 4108 a arewritten at intervals of about 4160 micrometers on a tape made ofaluminum. It is also possible to write the marks 4108 a at narrowerintervals. However, since the surface sensor 4109 used in thethirty-fourth embodiment is an inexpensive sensor with low resolutionusing a photodiode as a light-receiving element, the intervals cannot bemade narrower than this. The surface sensor 4109 irradiates light, whichis output from a not-shown light-emitting element, on the linear scale4108 and receives reflected light of the light with a not-shownlight-receiving element. Since the reflected light is intense in partswhere the marks 4108 a are not written and is weak in parts where themarks 4108 a are written, the marks 4108 a on the linear scale 4108 arerecognized according to a difference of an amount of received light.Although the aluminum tape is used as a base material for the linearscale 4108, the linear scale 4108 may be made of other materials.

When marks are provided by sticking the linear scale 4108 as in thethirty-fourth embodiment, as shown in FIG. 68A, usually, the linearscale 4108 is stuck such that both ends of the linear scale 4108 neveroverlap each other. Therefore, an interval of two marks opposed to eachother across this joint is much wider than the mark intervals on thelinear scale 4108. Thus, a mark detection signal part corresponding tothis joint part is a discontinuous part where an interval of signalparts corresponding to the marks is outside a range decided in advance,and a normal signal is not obtained.

FIG. 68B is an enlarged view of a part where a stain 4133 adheres on thelinear scale 4108 stuck on the belt 4106 in FIG. 66 or the drum 4126 inFIG. 67.

When the marks are provided on the surface side of the rotating body4106 or 4126 as in the thirty-fourth embodiment, stains of a toner orthe like may adhere to the marks. When the stains adhere in this way,reflected light of that part is weakened, and the part changes to adiscontinuous part where intervals of signal parts corresponding to themarks are outside a range decided in advance. Therefore, a normal signalis not obtained as in the case of the joint. Note that the same problemoccurs not only when stains adhere but also when the marks arescratched.

FIG. 69 is a block diagram of a structure of a control system thatsubjects angular displacement of motors 4120 and 4121 to digital controlbased on an output signal from the surface sensor 4109.

In FIG. 69, reference numeral 4135 denotes a microcomputer including amicroprocessor 4136, a read only memory (ROM) 4137, and a random accessmemory (RAM) 4138. The microprocessor 4136, the read only memory (ROM)4137, and the random access memory (RAM) 4138 are connected to oneanother via a bus 4143. Reference numeral 4139 denotes an instructiongenerating device that outputs a target instruction signal forinstructing target angular displacement of the motors 4102 and 4121. Theinstruction generating device 4139 is also connected to the bus 4143.Reference numeral 4142 denotes an interface device for detection thatprocesses an output pulse (mark detection signal) from the surfacesensor 4109 and converts the output pulse into a digital numericalvalue. The interface device for detection 4142 includes a counter, whichcounts the output pulse from the surface sensor 4109 every predeterminedsampling time, and sequentially sends count numbers of the counter tothe microcomputer 4135 via the bus 4143. Reference numeral 4140 denotesan interface for motor drive. The interface for motor drive 4140 outputsa pulse-like signal (control signal) for actuating a powersemiconductor, for example, a transistor constituting the motor drivedevice 4141 based on a result of comparison of a feedback signal sentfrom the microcomputer 4135 and a target instruction signal sent fromthe instruction generating device 4139. The motor drive device 4141operates based on the pulse-like signal from the interface for motordrive 4140 to control a voltage to be applied to the motors 4102 and4121.

Note that, in the thirty-fourth embodiment, the interface device fordetection 4142, the microcomputer 4135, the instruction generatingdevice 4139, and the interface for motor drive 4140 constitute afeedback control unit.

FIG. 70 is a block diagram of a schematic structure of a feedbackcontrol system according to the thirty-fourth embodiment. In the blockdiagram, a controller 4150 and a subtracter 4155 are constituted by theinterface for motor drive 4140 shown in FIG. 69. A plant 4151 includesan overall structure (drive device), which drives the motors 4102 and4121, the belt 4106, and the drum 4126, and the surface sensor 4109shown in FIGS. 66 and 67. A multiplying unit 4152 and a counter 4153 areconstituted by the interface device for detection 4142 shown in FIG. 69.In addition, a correction processing unit 4154 is constituted by themicrocomputer 4135. Note that a reference signal ref input to thesubtracter 4155 is equivalent to a target instruction signal output fromthe instruction generating device 4139.

In such a feedback control system, when the controller 4150 outputs acontrol signal to the motor drive device 4141 in the plant 4151, themotors 4102 and 4121 are driven to rotate at the number of revolutionscorresponding to the control signal. When this rotation drive force istransmitted to the belt 4106 or the drum 4126 in the plant 4151, and thebelt 4106 or the drum 4126 performs surface movement, the linear scale4108 moves endlessly following the surface movement. Then, the surfacesensor 4109 in the plant 4151 continuously detects the marks 4108 a onthe linear scale 4108 to thereby output an output pulse. When thisoutput pulse is input to the multiplying unit 4152 constituted by theinterface device for detection 4142, a frequency of the output pulse ismultiplied to be sixty-four times as large. The pulse multiplied to besixty-four times as large in this way (multiplied pulse) is input to thecounter 4153 constituted by the interface device for detection 4142. Thecounter 4153 counts a pulse number of the input multiplied pulse everypredetermined sampling time. This count number is input to thecorrection processing unit 4154 constituted by the microcomputer 4135.After performing correction processing to be described later, thecorrection processing unit 4154 outputs a feedback signal to thesubtracter 4155. The subtracter 4155 subtracts the feedback signal (themultiplied pulse or a dummy pulse to be described later) output from thecorrection processing unit 4154 from the reference signal ref, that is,the target instruction signal (target pulse number) input to thesubtracter 4155 and outputs a result of the subtraction to thecontroller 4150. The controller 4150 constituted by the interface formotor drive 4140 generates a control signal for controlling the motordrive device 4141 from the subtraction result and outputs the controlsignal to the motor drive device 4141 of the plant 4151. As a result,the belt 4106 or the drum 4126 is subjected to the feedback control suchthat a surface movement position thereof follows a target positioncorresponding to a target instruction signal generated by theinstruction generating device 4139.

FIG. 71 is a functional block diagram of a multiplying circuit thatconstitutes the multiplying unit 4152. This multiplying circuit usesPhase-Locked-Loop (PLL). More specifically, when an output pulse fromthe surface sensor 4109 is input, this output pulse is input to a phasecomparator 4160. A divided pulse from a frequency divider 4163 is alsoinput to the phase comparator 4160. The phase comparator 4160 performsphase comparison for the output pulse from the surface sensor 4109 andthe divided pulse from the frequency divider 4163 and outputs a voltageproportional to a phase difference of the output pulse and the dividedpulse. This output is input to a loop filter 4161 and smoothed. Anoutput of this loop filter 4161 is input to aVoltage-Controlled-Oscillator (VCO) 4162. The VCO 4162 controls afrequency of a pulse that is output according to a voltage output fromthe loop filter 4161. In the thirty-fourth embodiment, the VCO 4162outputs a multiplied pulse having a frequency sixty-four times as largeas the output pulse from the surface sensor 4109. This multiplied pulseis input to the counter 4153 as described above and, at the same time,feedbacked to the frequency divider 4163. The frequency divider 4163divides a frequency of the multiplied pulse from the VCO 4162 to afrequency inverse times of the multiple, that is, 1/64 as large. Thisdivided pulse is input to the phase comparator 4160.

In the next explanation, a discontinuous part is formed in an outputpulse from the surface sensor 4109 because a scratched or stained partof the linear scale 4108 or a joint of the scale is present in adetection area of the surface sensor 4109.

FIG. 72 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part when correction processing by thecorrection processing unit 4154 is not performed. In FIG. 72, ahorizontal axis indicates time and a vertical axis indicates a pulsenumber counted every sampling time for an output pulse from the surfacesensor 4109. The pulse number per sampling time is within a usual areaa1 in the figure for a continuous part. However, when the scratched orstained part of the linear scale 4108 or the joint of the scale reachesa detection area of the surface sensor 410, the surface sensor 4109cannot detect the marks 4108 a and the pulse number decreases as shownin the figure. Thus, in the thirty-fourth embodiment, when the pulsenumber per sampling time enters a range of an unusual area a2 deviatingfrom the usual area a1, the correction processing unit 4154 judges thatan error has occurred. Note that a designer can determine the usual areaa1 arbitrarily.

As an example of a method of determining a threshold pulse numberindicating a boundary of the usual area a1 and the unusual area a2, whenit is assumed thin sampling time is A, velocity of the belt 4106 or thedrum 4126 is B, resolution is C, and a mark interval (pitch of the marks4108 a) is D, the designer calculates a theoretical value fromcalculation of A×B×C÷D, determines a fluctuation width, which couldoccur due to usual disturbance, with respect to this value, and furtherdetermines the usual area a1 shown in FIG. 72 taking into account amargin equivalent to the fluctuation range. “Margin” in this context canbe determined from, for example, a distribution state of experimentaldata.

Pulse numbers Pn1, Pn2, and Pn3 at the time when the scratched orstained part or the joint part is not present in the detection area ofthe surface sensor 4109 are within the range of the usual area a1 inFIG. 72. However, when the scratched or stained part or the jointreaches the detection area of the surface sensor 4109, the pulse numbersfall to Pn4 and Pn5 to enter the range of the unusual area a2 in FIG.72. When the pulse numbers Pn4 and Pn5 (discontinuous part) are directlyused as a feedback signal, although the belt 4106 or the drum 4126 isdriven appropriately, it is judged that driving of the belt 4106 or thedrum 4126 has slowed down, and the belt 4106 or the drum 4126 issubjected to drive control to increase velocity. Then, when thediscontinuous part ends, it is judged that the driving of the belt 4106or the drum 4126 is fast because the velocity is increased in the errorpart (Pn6), and the belt 4106 or the drum 4126 is subjected to drivecontrol to decrease the velocity. Through such a series of driveoperations, the feedback system itself causes fluctuation, which is notpresent originally, and large fluctuation is caused in driving of thebelt 4106 or the drum 4126.

Thus, in the thirty-fourth embodiment, it is judged whether a pulsenumber counted every sampling time is within the range of the usual areaa1. If it is judged that the pulse number is not within the range of theusual area a1, that is, the pulse number is within the range of theunusual area a2, a dummy pulse is used as an alternative signal in theusual area a1 instead of the counted pulse number to continue thecontrol.

FIG. 73 is a flowchart of a flow of control in the feedback controlsystem according to the thirty-fourth embodiment. The surface sensor4109 detects the marks 4108 a on the linear scale 4108 (S1). Themultiplying unit 4152 multiplies a frequency of an output pulse from thesurface sensor 4109 to be a frequency sixty-four times as large (S2).Then, the counter 4153 counts a pulse number of the multiplied pulseevery sampling time (S3). The correction processing unit 4154 judgeswhether a count number output from the counter 4153 is within a definedrange, that is, whether the count number is equal to or larger than thethreshold pulse number (S4).

When the count number is within the defined range, since the countnumber is normal, the control unit additionally saves a count numbermeasured by the counter in the memory (check 1) in addition to a countnumber accumulated to that point (S5). Here, the memory (check 1) meansa specific saving area in the RAM 4138 shown in FIG. 69. Thereafter, thecontrol unit resets the counter (S6) and performs feedback control usingthe value additionally saved in the memory (check 1) (S7). Note that, aninitial value of the memory (check 1) is 0.

On the other hand, when it is judged in S4 that the count number is notwithin the defined range, the count number is an error valuecorresponding to a joint part or a scratched or stained part. Thus, inthe thirty-fourth embodiment, the control unit additionally saves apulse number of a dummy pulse in the memory (check 1) as a count number(S8). Thereafter, the control unit resets the counter (S6) and performsfeedback control using the value in the memory (check 1) in which thepulse number of the dummy pulse is additionally saved (S7).

Next, an example of determining a dummy pulse used in the correctionprocessing in the correction processing unit 4154 will be explained withreference to FIG. 74.

In FIG. 72, up to a pulse number Pn3, usual feedback control, in which acount number indicating the pulse number is directly used as a feedbacksignal, is performed. The pulse number at this point is saved in, forexample, the RAM 4138. When a count number of an output pulse from thesurface sensor 4109 is within the usual area a1, a value of the pulsenumber saved in the RAM 4138 is updated. When a pulse number Pn4 withinthe range of the unusual area a2 is counted, the pulse number (the pulsenumber Pn3 updated last) saved in the RAM 4138 is used as a pulse numberPn4 a of the dummy pulse instead of the pulse number Pn4. This pulsenumber is adopted as a feedback signal. This pulse number Pn4 a istreated as a counted pulse number in a control loop. The same holds truefor a pulse number Pn5. In this case, the value of the pulse numbersaved in the RAM 4138 is not updated, and the pulse number Pn3 updatedlast is held. Then, when a pulse number Pn6 in the usual area a1 iscounted, the processing returns to the usual feedback control. Byperforming such correction processing, even if the joint part or thescratched or stained part is present in a detection area of the surfacesensor 4109, a feedback control system does not become stable and thecontrol is continued.

Note that the method of determining a dummy pulse is not limited tothis, and other methods of determining a dummy pulse may be adopted.

According to the thirty-fourth embodiment, a pulse number is countedevery predetermined sampling time for a multiplied pulse obtained bymultiplying an output pulse from the surface sensor 4109 to besixty-four times as large. Therefore, the pulse number counted in thesampling time can be increased significantly compared with the time whenthe output pulse is not multiplied. This makes it possible to performhighly accurate feedback control. As a result, a maximum deviationamount between a position of the belt 4106 or the drum 4126 immediatelyafter a period of a discontinuous part ends and a target position can bereduced.

More specifically, as shown in FIG. 75A, in an output pulse beforemultiplication, when one pulse is present across a section timing T0 ofsampling time T1 or T2, this one pulse is counted in the sampling timeT1 when a pulse number is counted at a rising part of the pulse. In sucha case, if the sampling time T1 is started right in the rising part ofthe pulse, an advance position error equivalent to about ¾ of a markinterval occurs at this sampling time T1. In addition, if the samplingtime T2 is ended right in the rising part of the pulse, a delay positionerror equivalent to about ¼ of the mark interval occurs at this samplingtime T2. On the other hand, when the multiplied pulse obtained bymultiplying the output pulse is used as in the thirty-fourth embodiment,as shown in FIG. 75B, a position error, which could occur in samplingtime T1 or T2, is equivalent to 1/64 of the mark interval at themaximum. As a result, as shown in FIG. 76, an error range of a positionof the belt 4106 or the drum 4126 with respect to the target position,that is, an amplitude of a waveform in a period A or a period C1 can bereduced compared with the time when an output pulse is not multipliedshown in FIG. 75A. Consequently, a maximum delay amount D1 with respectto the target position of the belt 4106 or the drum 4126, which couldoccur immediately after the period B of the discontinuous part ends, canbe reduced compared with a maximum delay amount D2 in the time when anoutput pulse is not multiplied.

Next, a modification of the thirty-fourth embodiment will be explained.

In the thirty-fourth embodiment, since the multiplying circuit using PLLis used as the multiplying unit 4152, the multiplying unit 4152 includesthe loop filter 4161. Therefore, there is delay time equivalent to atime constant of the loop filter 4161. As a result of such delay time,even if a normal output pulse, that is, an output pulse having a pulsenumber within the range of the usual area a1 is input to the multiplyingunit 4152 after an abnormal output pulse, that is an output pulse havinga pulse number within the range of the unusual area a2 is input to themultiplying unit 4152 from the surface sensor 4109, a multiplied pulse apredetermined number times (sixty-four times) as large cannot begenerated instantly. Therefore, even if the normal output pulse isoutput from the surface sensor 4109, a normal multiplied pulse is notoutput from the multiplying unit 4152 in a period corresponding to thedelay time, and appropriate feedback control cannot be performed.

FIG. 77 is a timing chart for explaining a relation between an outputpulse output from the surface sensor 4109 and an operation of themultiplying part 4152. In this timing chart, an upper part indicates anoutput pulse output from the surface sensor 4109, a middle partschematically indicates a frequency of a multiplied pulse output fromthe multiplying unit 4152, and a lower part indicates an output signalof a timer to be described later.

If a joint part or a scratched or stained part is present in a detectionarea of the surface sensor 4109, as shown in the figure, a discontinuouspart, where marks are not detected in an output pulse from the surfacesensor 4109, is formed. In this case, it is assumed that a multipliedpulse is not output from the multiplying unit 4152 that multiplies theoutput pulse. Note that a multiplied pulse of a different frequency maybe output from the multiplying unit 4152. When the period B of thediscontinuous part ends, an output pulse is output from the surfacesensor 4109 again. However, the multiplying unit 4152 cannot output amultiplied pulse multiplied to be the predetermined number times(sixty-four times) as large immediately due to the time constant of theloop filter 4161. In other words, even after the period B of thediscontinuous part ends, an appropriate multiplied pulse is not outputfrom the multiplying unit 4152 during a period E in the figure.Therefore, if a pulse number used in the correction processing unit 4154is switched from a dummy pulse number to a pulse number of a multipliedpulse immediately after the period B of the discontinuous part ends, itis likely that appropriate feedback control cannot be performed.

FIG. 78 is a flowchart of a flow of control in a feedback control systemaccording to this modification.

In this modification, when the correction processing unit 4154 judgesthat a count number of a multiplied pulse output from the counter 4153is not within a defined range (S4), the correction processing unit 4154starts a timer. This timer is constituted by a not-shown timer circuitprovided outside the microcomputer 4135 shown in FIG. 69. Thus, themicrocomputer 4135, which has judged that the count number is not withinthe defined range, sends a measurement signal to the timer circuit. Thetimer circuit, which has received the measurement signal, measures timeuntil a set time. As shown in FIG. 77, the timer circuit outputs anoutput signal of an L level to the microcomputer 4153 when the timerstarts the measurement of time and outputs an output signal of an Hlevel when the time has reached the set time. Note that, thereafter,while it is judged that a count number is within the defined range, thecorrection processing unit 4154 never restarts the timer even if it isjudged that a count number is not within the defined range. Note that,although the set time is measured using the timer circuit in thismodification, other means may be used as long as the means can measuretime.

When the correction processing unit 4154 judges that the count number iswithin the defined range (S4), the correction processing unit 4154judges whether the timer has reached the set time based on an outputsignal from the timer circuit (S9). When the correction processing unit4154 judges that the time has not reached the set time, the feedbackcontrol system continues feedback control using a dummy pulse in thesame manner as at the time when the correction processing unit 4154judges that the count number is not within the defined range in S4 (S8,S6, and S7). Thereafter, when the correction processing unit 4154 judgesthat the timer has reached the set time (S9), the feedback controlsystem returns to the usual feedback control (S5, S6, and S7).Therefore, if the set time of the timer is set larger than the timeobtained by adding the period E to the period B shown in FIG. 77, thefeedback control system can perform appropriate feedback control withoutbeing affected by delay time of the multiplying unit 4152. Note thatthis set time only has to be equal to or larger than the time obtainedby adding the period E to the period B shown in FIG. 77. However, inthis modification, the set time is set to be time F equivalent to timeinteger times as long as the sampling time. This makes it possible touse a reference clock, which is used to measure the sampling time, inthe time circuit as well and not to use a clock generating circuit inrealizing the feedback control system. Note that, in this modification,since the period B is also time equivalent to time integer times as longas the sampling time, time obtained by deducting time equivalent to theperiod B from the time F (operation stable period) is also timeequivalent to time integer times as large as the sampling time.

In this modification, the microcomputer 4135 constituting the correctionprocessing unit 4154 functions as a control switching unit that performsswitching processing for switching feedback control using a multipliedpulse and feedback control using a dummy pulse based on an output signalfrom the timer circuit. More specifically, a program for causing themicroprocessor 4136 constituting the microcomputer 4135 to function asthe control switching unit is stored in the ROM 4137 serving as aprogram storing medium, and the microprocessor 4136 reads out andexecutes this program, whereby the switching processing is performed.

Although this switching processing is realized by software in thismodification, the switching processing may be realized by hardware. Forexample, the interface device for detection 4142, which processes anoutput pulse from the surface sensor 4109 and converts the output pulseinto a digital numerical value, may be functioned as the controlswitching unit. In this case, for example, the interface device fordetection 4142 judges a discontinuous part in the same manner as thecorrection processing unit 4154 from the output pulse from the surfacesensor 4109 and prevents the output pulse from being input to themultiplying unit 4152 until the set time after the period B of thediscontinuous part starts.

It is also possible to continue the feedback control using a dummy pulseuntil time equivalent to the set time without using the timer circuit.As a specific example, a light receiving level of the surface sensor4109 before and after the discontinuous part is as indicated by a solidline shown in an upper part of FIG. 79. When this light receiving levelsignal is passed through a low pass filter, a low frequency signal asindicated by an alternate long and short dash line shown in the upperpart of FIG. 79. Then, a signal level of this low frequency signal and apredetermined threshold level S are compared to generate a comparisonresult signal shown in a middle part of FIG. 79. This comparison resultsignal is at an H level if the signal level of the low frequency signalis equal to or higher than the predetermined threshold level S and at anL level if the signal level of the low frequency signal is lower thanthe predetermined threshold level S. This comparison result signal isoutput to the correction processing unit 4154 after being delayed by adelay circuit or the like. Through this delay, an L level end time ofthe delay signal input to the correction processing unit 4154 is madecoincident with an end of the period F shown in FIG. 77. If the surfacesensor 4109 constituted in this way is used, the correction processingunit 4154 judges whether this delay signal is at the L level instead ofthe judgment in S9 shown in FIG. 78. Consequently, it is possible tocause the surface sensor 4109 to continue the feedback control using adummy pulse until the time equivalent to the set time without using thetimer circuit.

As described above, the drive control device in the thirty-fourthembodiment detects the marks 4108 a, which are provided to continue atthe predetermined intervals over the endless moving direction of thebelt 4106 or the drum 4126 serving as a drive control object member,which moves endlessly, or the drive roller 4101, the driven roller 4104or 4105, or the driven pulley 4128 serving as an endless moving memberendlessly moving following the endless movement of the belt 4106 or thedrum 4126, with the surface sensor 4109 serving as mark detecting means.Then, the drive control device feedback-controls driving of the belt4106 or the drum 4126 using an output pulse that is a mark detectionsignal obtained by the detection. The drive control device includes theinterface device for detection 4142 constituting the multiplying unit4152 serving as multiplying means that generates a multiplied pulse,which is a multiplied signal obtained by multiplying the output pulse tobe predetermined times as large. In addition, the drive control devicealso includes the interface device for detection 4142 serving asfeedback control means, which performs feedback control using amultiplied pulse when it is judged that a discontinuous part in whichintervals of signal parts corresponding to marks are outside the rangedecided in advance (usual area a1) is not present in an output pulse ora multiplied signal and performs feedback control using a multipliedpulse when the discontinuous part is present, the microcomputer 4135,the instruction generating device 4139, and the interface for motordrive 4140. With such a structure, as described above, even if thesurface sensor 4109 is a surface sensor with low resolution, there is aneffect of improving dummy resolution. In addition, concerning acontinuous part in an output pulse or a multiplied pulse, an error rangeof a position of the belt 4106 or the drum 4126 with respect to a targetposition can be reduced. As a result, an amount of maximum deviation D1,which could occur immediately after the period B of the discontinuouspart ends, can be reduced. Therefore, rapid velocity variation in thebelt 4106 or the drum 4126, which could occur immediately after theperiod B of the discontinuous part ends, can be controlled. In addition,a period C1, which is required until velocity of the belt 4106 or thedrum 4126 stabilizes after the end of the period B of the discontinuouspart, can also be reduced.

In the thirty-fourth embodiment, the feedback control system uses thePLL circuit serving as a multiplying circuit, which compares phases of afeedbacked multiplied pulse and an output pulse before multiplicationand generates a multiplied pulse using a result of the phase comparison.This makes it possible to generate a multiplied pulse with aninexpensive structure.

In the thirty-fourth embodiment, the feedback control system has thecontrol switching unit that performs switching processing for switchingselection concerning whether to cause the feedback control unit toperform feedback control using a multiplied pulse or to perform feedbackcontrol using a dummy pulse. Consequently, a period in which thefeedback control unit is caused to perform feedback control using adummy pulse is set as a period obtained by adding an operationstabilizing period, which is set to be equal to or longer than time Enecessary for a multiplication operation by the multiplying circuit tostabilize, to period B from the time when it is judged that thediscontinuous part is present until the time when the discontinuous partis not present. As a result, as described above, the feedback controlmeans can perform appropriate feedback control without being affected bydelay time of the multiplying circuit as described above.

In the thirty-fourth embodiment, the judgment on whether thediscontinuous part is present depends on whether a count number, whichis the number of signal parts corresponding to marks in an output pulseor a multiplied pulse obtained in predetermined sampling time, is lessthan a defined number. The operation stabilizing period is set to aperiod equivalent to time integer times as long as the sampling time.This makes it possible not to use the clock generating circuit andrealize cost reduction as described above.

In the thirty-fourth embodiment, the feedback control system has the ROM4137 serving as a program storing medium having stored therein a programfor causing the microprocessor 4136 of the computer 4135 functioning asthe feedback control unit to function as the control switching means.The microprocessor 4136 performs the switching processing by executingthis program. By performing the switching processing on software in thisway, since it is unnecessary to provide hardware functioning as thecontrol switching unit separately, cost reduction can be realized.

As described above, the control switching unit may be constituted toperform the switching processing by sending a switching signal to thefeedback control unit. With such as structure, the switching processingcan also be performed.

Next, a thirty-fifth embodiment of the invention will be explained.Since a basic structure in the thirty-fifth embodiment is the same asthat in the thirty-fourth embodiment, only different parts will beexplained.

A drive control device in the thirty-fifth embodiment detects the marks4108 a, which are provided to continue at the predetermined intervalsover the endless moving direction of the belt 4106 or the drum 4126serving as a drive control object member, which moves endlessly, or thedrive roller 4101, the driven roller 4104 or 4105, or the driven pulley4128 serving as an endless moving member endlessly moving following theendless movement of the belt 4106 or the drum 4126, with the surfacesensor 4109 serving as mark detecting means. Then, the drive controldevice feedback-controls driving of the belt 4106 or the drum 4126 usingan output pulse that is a mark detection signal obtained by thedetection.

In the thirty-fourth embodiment, it is likely that, even if the feedbackcontrol is applied to a discontinuous part in a mark detection signalusing an alternative signal, a signal part immediately before or afterthe discontinuous part is made unstable and appropriate drive controlcannot be performed in that signal part. Thus, the thirty-fifthembodiment describes a more improved example.

FIG. 80A is an enlarged view of a joint part of the linear scale 4108stuck on a surface of a drive control member. The plural marks 4108 aare provided at equal intervals in an endless moving direction on a tapemade of aluminum. A not-shown surface sensor serving as mark detectingmeans irradiates light emitted from a light-emitting element on thelinear scale 4108 and receives reflected light of the light with alight-receiving element. Since the reflected light is intense in partswhere the marks 4108 a are not written and is weak in parts where themarks 4108 a are written, the marks 4108 a on the linear scale 4108 arerecognized according to a difference of an amount of received light.Although the aluminum tape is used as a base material for the linearscale 4108, the linear scale 4108 may be made of other materials. Whenmarks are provided by sticking the linear scale 4108 as in this way, asshown in FIG. 80A, usually, the linear scale 4108 is stuck such thatboth ends of the linear scale 4108 never overlap each other. Therefore,an interval of two marks opposed to each other across this joint is muchwider than the mark intervals on the linear scale 4108. Since lightreflectance on the surface of the drive control object member is usuallylower than that on the surface of the linear scale, as shown in FIG.80B, a light receiving level in a part corresponding to the joint part4132 falls. As a result, in a mark detection signal shown in FIG. 80Cobtained by forming this light receiving level in a pulse shape using apredetermined threshold value, there is a discontinuous part whereintervals of signal parts (H level parts) corresponding to marks areoutside a range decided in advance. Therefore, in the thirty-fourthembodiment, as described above, the feedback control is applied to thisdiscontinuous part using an alternative signal as a mark detectionsignal.

However, when the joint part 4132 shown in FIG. 80A passes a detectionarea of the surface sensor, a light receiving level is made unstable asin a part encircled by a broken line in FIG. 80B immediately after thepassage. This is caused by influence of charging time or the like of acapacitor provided in an electric circuit of the surface sensor. In thepart where the light receiving level is unstable in this way, as shownin FIG. 80C, a duty ratio of a mark detection signal is broken, and themark detection signal is made unstable. As a result, even if thealternative signal is used only for the discontinuous part, appropriatefeedback control cannot be performed in some cases.

FIG. 81A is an enlarged view of the joint part of the linear scale 4108stuck on the surface of the drive control object member as in FIG. 80A.An end of the linear scale 4108 stuck on the surface of the drivecontrol object member may be turned up as shown in FIG. 81B due to useof the drive control object member over time. In such a turned-up part4108 b, a reflecting direction of light from a light-emitting elementvaries depending on how the part is turned up. Thus, a light receivinglevel is made unstable in a part corresponding to the turned-up part asindicated by a broken line in FIG. 81B. In the part where the lightreceiving level is unstable in this way, as shown in FIG. 81C, a dutyratio of a mark detection signal is broken, and the mark detectionsignal is made unstable. As a result, even if the alternative signal isused only for the discontinuous part, appropriate feedback controlcannot be performed in some cases.

Note that this turned-up part 4108 b could be formed at both ends of thelinear scale 4108. Therefore, when the turned-up part 4108 b is formedat the end of the linear scale 4108 on the left side in FIG. 81B, anunstable mark detection signal with a broken duty ratio also appears ona start side (left side in FIG. 81C) of the discontinuous part.

FIG. 82A is an enlarged view of a stain part 133 adhering on the linearscale 4108 stuck on a surface of a drive control object member. Asdescribed above, a stain may adhere to a part of marks on the linearscale 4108. Since light reflectance is generally low in this stain part133, as shown in FIG. 82B, a light receiving level in a partcorresponding to the stain part 133 falls. As a result, in a markdetection signal, there is a discontinuous part where intervals ofsignal parts (H level parts) corresponding to marks are outside a rangedecided in advance. Therefore, in the thirty-fourth embodiment, asdescribed above, the feedback control is applied to this discontinuouspart using an alternative signal as a mark detection signal.

However, when powder like a toner hardens to form the stain part 133,the powder may spread and adhere around the stain part 133. In a powderpart 133 a spread in this way, a light receiving level in a partcorresponding to the powder part 133 a is made unstable as indicated bya broken line in FIG. 82B. In the part where the light receiving levelis unstable in this way, a duty ratio of a mark detection signal isbroken, and the mark detection signal is made unstable. As a result,even if the alternative signal is used only for the discontinuous part,appropriate feedback control cannot be performed in some cases.

FIGS. 83A and 83B are block diagrams of structures of a control systemthat subjects angular displacement of the motors 4102 and 4121 todigital control based on an output signal from the surface sensor 4109.In FIGS. 83A and 83B, reference numeral 4135 denotes a microcomputerincluding the microprocessor 4136, the read only memory (ROM) 4137, andthe random access memory (RAM) 4138. The microprocessor 4136, the readonly memory (ROM) 4137, and the random access memory (RAM) 4138 areconnected to one another via the bus 4143. Reference numeral 4139denotes an instruction generating device that outputs a targetinstruction signal for instructing target angular displacement of themotors 4102 and 4121. The instruction generating device 4139 is alsoconnected to the bus 4143. Reference numeral 4142 denotes an interfacedevice for detection that processes an output pulse (mark detectionsignal) from the surface sensor 4109 and converts the output pulse intoa digital numerical value. The interface device for detection 4142includes a counter, which counts the output pulse from the surfacesensor 4109 every predetermined sampling time, and sequentially sendscount numbers of the counter to the microcomputer 4135 via the bus 4143.The microcomputer 4135 multiplies the count value by a conversionconstant of pulse number versus angular displacement decided in advanceto obtain angular displacement of the rotation shaft of the motor 4102.Reference numeral 4140 denotes an interface for motor drive. Theinterface for motor drive 4140 outputs a pulse-like signal (controlsignal) for actuating a power semiconductor, for example, a transistorconstituting the motor drive device 4141 based on a result of comparisonof a feedback signal sent from the microcomputer 4135 and a targetinstruction signal sent from the instruction generating device 4139. Themotor drive device 4141 operates based on the pulse-like signal from theinterface for motor drive 4140 to control a voltage to be applied to themotors 4102 and 4121. Reference numeral 4144 denotes a current sensorthat detects a motor drive current flowing to the motors 4102 and 4121.A result of the detection of the current sensor 4144 is sent to themicrocomputer 4135 via an interface device for motor drive current 4145.

In FIG. 83B, a mechanism for detecting angular velocity of the motors4102 and 4121 is further provided. More specifically, an angularvelocity detector 4146 is provided for the motors 4102 and 4121. Theangular velocity detector 4146 counts an output pulse from an encoderprovided in the rotation shafts of the motors 4102 and 4121 everypredetermined time and detects angular velocity of the motors 4102 and4121 from a value of the count and passing time of a pulse width. Aresult of the detection is sent to the microcomputer 4135 via aninterface device for motor angular speed 4147.

Note that, in the thirty-fifth embodiment, the interface device fordetection 4142, the microcomputer 4135, the instruction generatingdevice 4139, and the interface for motor drive 4140 constitute afeedback control unit.

FIG. 84 is a control block diagram of a schematic structure of afeedback control system according to the thirty-fifth embodiment. Inthis block diagram, the controller 4150 and the subtracter 4155 areconstituted by the interface for motor drive 4140 shown in FIGS. 83A and83B. The plant 4151 includes an overall structure (drive device), whichdrives the motors 4102 and 4121, the belt 4106, and the drum 4126, andthe surface sensor 4109 shown in FIGS. 66 and 67. The multiplying unit4152 and the counter 4153 are constituted by the interface device fordetection 4142 shown in FIGS. 83A and 83B. In addition, the correctionprocessing unit 4154 is constituted by the microcomputer 4135. Note thata reference signal ref input to the subtracter 4155 is equivalent to atarget instruction signal output from the instruction generating device4139.

In such a feedback control system, when the controller 4150 outputs acontrol signal to the motor drive device 4141 in the plant 4151, themotors 4102 and 4121 are driven to rotate at the number of revolutionscorresponding to the control signal. When this rotation drive force istransmitted to the belt 4106 or the drum 4126 in the plant 4151, and thebelt 4106 or the drum 4126 performs surface movement, the linear scale4108 moves endlessly following the surface movement. Then, when thesurface sensor 4109 in the plant 4151 continuously detects the marks4108 a on the linear scale 4108, a light receiving level of a lightreceiving element thereof is as shown in FIG. 85A due to a difference ofreflectance on a scale surface and mark parts. As shown in FIG. 85B, thesurface sensor 4109 outputs a pulse signal (output pulse) serving as amark detection signal that is at an H level when the light receivinglevel is equal to or lower than a threshold value set in advance and atan L level when the light receiving level is larger than the thresholdvalue. When this output pulse is input to the multiplying unit 4152constituted by the interface device for detection 4142, a frequency ofthe output pulse is multiplied to be sixty-four times as large. Thepulse multiplied to be sixty-four times as large (multiplied pulse) inthis way is input to the counter 4153 constituted by the interfacedevice for detection 4142. The counter 4153 counts a pulse number of theinput multiplied pulse every predetermined sampling time. This countnumber is input to the correction processing unit 4154 constituted bythe microcomputer 4135. After performing correction processing to bedescribed later, the correction processing unit 4154 outputs a feedbacksignal to the subtracter 4155. The subtracter 4155 subtracts thefeedback signal (the multiplied pulse or a dummy pulse to be describedlater) output from the correction processing unit 4154 from thereference signal ref, that is, the target instruction signal (targetpulse number) input to the subtracter 4155 and outputs a result of thesubtraction to the controller 4150. The controller 4150 constituted bythe interface for motor drive 4140 generates a control signal forcontrolling the motor drive device 4141 from the subtraction result andoutputs the control signal to the motor drive device 4141 of the plant4151. As a result, the belt 4106 or the drum 4126 is subjected to thefeedback control such that a surface movement position thereof follows atarget position corresponding to a target instruction signal generatedby the instruction generating device 4139.

FIG. 89 is a functional block diagram of a multiplying circuit thatconstitutes the multiplying unit 4152. This multiplying circuit usesPhase-Locked-Loop (PLL). More specifically, when an output pulse fromthe surface sensor 4109 is input, this output pulse is input to thephase comparator 4160. A divided pulse from the frequency divider 4163is also input to the phase comparator 4160. The phase comparator 4160performs phase comparison for the output pulse from the surface sensor4109 and the divided pulse from the frequency divider 4163 and outputs avoltage proportional to a phase difference of the output pulse and thedivided pulse. This output is input to a loop filter 4161 and smoothed.An output of this loop filter 4161 is input to theVoltage-Controlled-Oscillator (VCO) 4162. The VCO 4162 controls afrequency of a pulse that is output according to a voltage output fromthe loop filter 4161. In the thirty-fifth embodiment, the VCO 4162outputs a multiplied pulse having a frequency sixty-four times as largeas the output pulse from the surface sensor 4109. This multiplied pulseis input to the counter 4153 as described above and, at the same time,feedbacked to the frequency divider 4163. The frequency divider 4163divides a frequency of the multiplied pulse from the VCO 4162 to afrequency inverse times of the multiple, that is, 1/64 as large. Thisdivided pulse is input to the phase comparator 4160.

In the next explanation, a discontinuous part is formed in an outputpulse from the surface sensor 4109 because a scratched or stained partof the linear scale 4108 or a joint of the scale is present in adetection area of the surface sensor 4109.

FIG. 87 is a graph of a pulse number to be counted every sampling timebefore and after a discontinuous part when correction processing by thecorrection processing unit 4154 is not performed. In FIG. 87, ahorizontal axis indicates time and a vertical axis indicates a pulsenumber counted every sampling time for an output pulse from the surfacesensor 4109. The pulse number per sampling time is within a usual areaa1 in the figure for a continuous part. However, when the scratched orstained part of the linear scale 4108 or the joint of the scale reachesa detection area of the surface sensor 410, the surface sensor 4109cannot detect the marks 4108 a and the pulse number decreases as shownin the figure. Thus, in the thirty-fifth embodiment, when the pulsenumber per sampling time enters a range of an unusual area a2 deviatingfrom the usual area a1, the correction processing unit 4154 judges thatan error has occurred. Note that a designer can determine the usual areaa1 arbitrarily.

As an example of a method of determining a threshold pulse numberindicating a boundary of the usual area a1 and the unusual area a2, whenit is assumed thin sampling time is A, velocity of the belt 4106 or thedrum 4126 is B, resolution is C, and a mark interval (pitch of the marks4108 a) is D, the usual area a1 as shown in FIG. 87 is determined from atheoretical value calculated from the expression A×B×C÷D.

Pulse numbers Pn1, Pn2, and Pn3 at the time when the scratched orstained part or the joint part is not present in the detection area ofthe surface sensor 4109 are within the range of the usual area a1 inFIG. 87. However, when the scratched or stained part or the joint partreaches the detection area of the surface sensor 4109, the pulse numbersfall to Pn4 and Pn5 to enter the range of the unusual area a2 in FIG.87. When the pulse numbers Pn4 and Pn5 (discontinuous part) are directlyused as a feedback signal, although the belt 4106 or the drum 4126 isdriven appropriately, it is judged that driving of the belt 4106 or thedrum 4126 has slowed down, and the belt 4106 or the drum 4126 issubjected to drive control to increase velocity. Then, when thediscontinuous part ends, it is judged that the driving of the belt 4106or the drum 4126 is fast because the velocity is increased in the errorpart (Pn6), and the belt 4106 or the drum 4126 is subjected to drivecontrol to decrease the velocity. Through such a series of driveoperations, the feedback system itself causes fluctuation, which is notpresent originally, and large fluctuation is caused in driving of thebelt 4106 or the drum 4126.

In the thirty-fifth embodiment, it is judged whether a pulse numbercounted every sampling time is within the range of the usual area a1. Ifit is judged that the pulse number is not within the range of the usualarea a1, that is, the pulse number is within the range of the unusualarea a2, a dummy pulse is used as an alternative signal in the usualarea a1 instead of the counted pulse number to continue the control.

As a result of researches by the inventors, it was found that, even if adummy pulse is used only for a discontinuous part, appropriate drivecontrol cannot be performed immediately before and after thediscontinuous part in some cases. This is caused by influence ofcharging time or the like of a capacitor provided in an electric circuitof the surface sensor 4109 as shown in FIG. 80, turn-up of an end of thelinear scale 4108 as shown in FIG. 81, powder spread around a stain partas shown in FIG. 82, and the like.

Thus, in the thirty-fifth embodiment, control is performed using a dummypulse not only in a discontinuous part but also in parts immediatebefore and after the discontinuous part such that appropriate drivecontrol can be performed immediately before and after the discontinuouspart even if such causes occur.

A first operation example will be explained. In the explanation,appropriate drive control cannot be performed immediately after adiscontinuous part due to influence of charging time or the like of thecapacitor provided in the electric circuit of the surface sensor 4109 asshown in FIG. 80 (this operation example will be hereinafter referred toas “first operation example”).

Due to influence of charging time or the like of the capacitor providedin the electric circuit of the surface sensor 4109, immediately after adiscontinuous part, a light receiving level is made unstable asindicated by a broken line in FIG. 85A and an output pulse is also madeunstable as shown in FIG. 85B. Note that FIG. 85C shows a mark controlsignal (specific control signal) that is an output signal of a timerserving as specific control signal output means to be described later.

FIG. 88 is a flowchart of a flow of control in a feedback control systemin this first operation example. The surface sensor 4109 detects themarks 4108 a on the linear scale 4108 (S1). The multiplying unit 4152multiplies a frequency of an output pulse from the surface sensor 4109to be sixty-four times as large (S2). The counter 4153 counts a pulsenumber of the multiplied pulse every sampling time (S3). The correctionprocessing unit 4154 judges whether a count number output from thecounter 4153 is within a defined range, that is, whether the countnumber is equal to or larger than the threshold pulse number (thresholdvalue) (S4).

When the count number is within the defined range, next, the feedbackcontrol system judges whether a timer started to count time as describedlater has reached set time (S5). Here, since the timer has not startedyet, considering that the count number is normal, the feedback controlsystem additionally saves the count number measured by the counter inaddition to a count number accumulated to that point in the memory(check 1) (S6). The memory (check 1) means a specific saving area of theRAM 4138 shown in FIGS. 83A and 83B. Thereafter, the feed back controlsystem reset the counter (S7) and performs feedback control using avalue in the memory (check 1) in which the count number is additionallysaved (S8). Note that an initial value of the memory (check 1) is 0.

On the other hand, when it is judged in S4 that the count number is notwithin the defined range, the count number is an error valuecorresponding to a joint part or a scratched or stained part. In thiscase, in the first operation example, first, the feedback control systemstarts the timer (S9). This timer is constituted by a not-shown timercircuit provided outside the microcomputer 4135 shown in FIGS. 83A and83B. Thus, the microcomputer 4135, which has judged that the countnumber is not within the defined range, sends a measurement signal tothe timer circuit, and the timer circuit, which has received themeasurement signal, measures time until set time (fixed time). Inaddition, as shown in FIG. 85C, the timer circuit outputs an outputsignal of an L level to the microcomputer 4135 when the measurement oftime is started and outputs an output signal of an H level after the settime. Note that, thereafter, while it is judged that a count number iswithin the defined range, the feedback control system never restarts thetimer even if it is judged that a count number is within the definedrange. Although the set time is measure using the timer circuit in thefirst operation example, other means may be used as long as the meanscan measure time.

When the timer is started in this way, the feedback control systemadditionally saves a pulse number of a dummy pulse in the memory (check1) as a count number (S10). Then, the feedback control system resets thecounter (S7) and performs the feedback control using a value in thememory (check 1) in which the count number is additionally saved (S8).Thereafter, when the correction processing unit 4154 judges that a countnumber is within the defined range (S4), the correction processing unit4154 judges whether the timer has reached the set time using an outputsignal from the timer circuit (S5). When it is judged in this judgmentthat the time has not reached the set time yet, the feedback controlsystem continues the feedback control using a dummy pulse in the samemanner as at the time when the count number is not within the definedrange in S4 (S10, S7, and S8). Then, when the feedback control systemjudges that the time has reached the set time (S5), the feedback controlsystem returns to the usual feedback control (S6, S7, and S8).Therefore, if the set time for the timer is set to time obtained byadding a period B immediately after a part where an unstable signal partis present in an output pulse to a period A of a discontinuous part asshown in FIG. 85C, the feedback control system can perform appropriatefeedback control without being affected by charging time or the like ofthe capacitor provided in the electric circuit of the surface sensor4109.

Note that, even if the set time is a part of the period B in which anunstable signal part is present in an output pulse, sufficient effectcan be shown. This is because influence of charging time or the like ofthe capacitor provided in the electric circuit of the surface sensor4109 is larger when time from the discontinuous part is shorter. Inother words, in the period in which an unstable signal part is presentin an output pulse, a former half part in which time from thediscontinuous part is short is significantly affected by charging timeor the like of the capacitor. Thus, if control using a dummy pulse isapplied to the former half part, influence of charging time or the likeof the capacitor as a whole can be controlled significantly. Inaddition, this set time may be longer than the period B in which anunstable signal part is present in an output pulse to secure a margintaking into account an error.

In addition, it is desirable that the set time is set to be timeequivalent to integer times as long as the sampling time. This makes itpossible to use a reference clock, which is used for measuring thesampling time, in the timer circuit as well and not to provide a clockgenerating circuit in realizing the feedback control system.

Next, an example of a method of determining a dummy pulse used in thecorrection processing in the correction processing unit 4154 will beexplained with reference to FIG. 89.

In FIG. 87, up to a pulse number Pn3, the usual feedback control, inwhich a count number indicating the pulse number is used directly as afeedback signal, is performed. The pulse number at this point is savedin, for example the RAM 4138. When a count number of an output pulsefrom the surface sensor 4109 is within the usual area a1, a value of thepulse number saved in the RAM 4138 is updated. Then, when a pulse numberPn4 within the unusual area a2 is counted, the pulse number saved in theRAM 4138 (the pulse number Pn3 updated last) is used as a pulse numberPn4 a of a dummy pulse instead of the pulse number PN4 and is adopted asa feedback signal. This pulse number Pn4 a is treated as a counted pulsenumber in a control loop. The same holds true for a pulse number Pn5. Inthis case, the value of the pulse number saved in the RAM 4138 is notupdated, and the pulse number Pn3 updated last is held. Moreover, untilthe set time elapses after the count number enters the usual area a1,the pulse number is used as pulse numbers Pn6 a and Pn7 a of a dummypulse and is adopted as a feedback signal. In this case, again, thevalue of the pulse number saved in the RAM 4138 is not updated, and thepulse number Pn3 updated last is held. Then, when the set time haselapsed, the processing returns to the usual feedback control. Byperforming such correction processing, even if a joint part or ascratched or stained part is present in the detection area of thesurface sensor 4109, the feedback control system is not made unstable,and the control is continued. Moreover, appropriate feedback control canbe performed without being affected by charging time or the like of thecapacitor provided in the electric circuit of the surface sensor 4109.

Note that the method of determining a dummy pulse is not limited tothis, and other methods of determining a dummy pulse may be adopted.

According to the first operation example (the same holds true foroperation examples to be described later), a pulse number is countedevery predetermined sampling time for a multiplied pulse that isobtained by multiplying an output pulse from the surface sensor 4109 tobe sixty-four times as large. Therefore, a pulse number to be counted inthe sampling time can be increased significantly compared with the timewhen an output pulse is not multiplied. This makes it possible toperform highly accurate feedback control. As a result, a maximumdeviation amount between a position of the belt 4106 or the drum 4126immediately after a period of a discontinuous part ends and a targetposition can be reduced.

More specifically, as shown in FIG. 90A, in an output pulse beforemultiplication, when one pulse is present across a section timing T0 ofsampling time T1 or T2, this one pulse is counted in the sampling timeT1 when a pulse number is counted at a rising part of the pulse. In sucha case, if the sampling time T1 is started right in the rising part ofthe pulse, an advance position error equivalent to about ¾ of a markinterval occurs at this sampling time T1. In addition, if the samplingtime T2 is ended right in the rising part of the pulse, a delay positionerror equivalent to about ¼ of the mark interval occurs at this samplingtime T2. On the other hand, when the multiplied pulse obtained bymultiplying the output pulse is used as in the first operation example,as shown in FIG. 90B, a position error, which could occur in samplingtime T1 or T2, is equivalent to 1/64 of the mark interval at themaximum. As a result, an error range of a position of the belt 4106 orthe drum 4126 with respect to the target position can be reducedcompared with the time when an output pulse is not multiplied.

In the first operation example, the microcomputer 4135 constituting thecorrection processing unit 4154 functions as a feedback control unitthat judges whether a discontinuous part is present in an output pulsebased on an output signal from the timer circuit, when it is judged thata discontinuous part is present in the output pulse, applies feedbackcontrol using a dummy pulse instead of the output pulse to thediscontinuous part, and also applies the feedback control to at least apart of an unstable signal part present immediately after thediscontinuous part using the dummy pulse. More specifically, a programfor causing the microprocessor 4136 constituting the microcomputer 4135to function as the feedback control unit is stored in the ROM 4137serving as a program storing medium. The microprocessor 4136 reads outand executes this program, whereby processing by the feedback controlunit is performed.

Although the processing by the feedback control unit is realized bysoftware in the first operation example, the processing may be realizedby hardware. For example, the interface device for detection 4142, whichprocesses an output pulse from the surface sensor 4109 and converts theoutput pulse into a digital numerical value, is used as a part of thefeedback control unit. In this case, for example, the interface devicefor detection 4142 judges a discontinuous part in the same manner as thecorrection processing unit 4154 from the output pulse from the surfacesensor 4109 and prevents the output pulse from being input to themultiplying unit 4152 from the start of the period A of thediscontinuous part until the set time.

In addition, in the first operation example, a cause of inappropriatecontrol is not limited to the influence of charging time or the like ofthe capacitor provided in the electric circuit of the surface sensor4109. The same explanation as above can be applied at the time when anunstable signal part is present in an output pulse immediately after theperiod A of the discontinuous part ends due to the turn-up at the end ofthe linear scale 4108 as shown in FIG. 81, the powder spread around thestain part as shown in FIG. 82, and the like.

A second operation example will be explained. In the second operationexample, the turn-up at the end of the linear scale 4108 as shown inFIG. 81 occurs on a downstream side in an endless moving direction of ajoint, and appropriate drive control cannot be performed immediatelybefore a discontinuous part (this operation example will be hereinafterreferred to as “second operation example”).

Due to the turn-up at the end of the linear scale 4108, immediatelybefore the discontinuous part, a light receiving level is made unstableas indicated by a broken line in FIG. 91A, and an output pulse is alsomade unstable as shown in FIG. 91B. Note that FIG. 91C shows a markcontrol signal (specific control signal) as in the first operationexample. The second operation example will be explained assuming thatthere is an unstable signal part only in a part immediately before thediscontinuous part and there is no unstable signal part immediate afterthe discontinuous part.

FIG. 92 is a flowchart of a flow of control in a feedback control systemin the second operation example. Since a basic flow of the feedbackcontrol in the second operation example is the same as that in the firstoperation example, only points different from the first operationexample will be hereinafter explained.

In the second operation example, before the correction processing unit4154 judges whether a count number output from the counter 4153 iswithin a defied range (S4), the feedback control system judges whetherthe feedback control system is presently in a correction processingperiod to be described later (fixed period) (S11). Here, the correctionprocessing time has not been set yet, the correction processing unit4154 judges whether the count number is within the defined range as inthe first operation example (S4). When it is judged that the countnumber is not within the defined range, the count number is an errorvalue substantially corresponding to a boundary between the linear scale4108 where turn-up at the end thereof has occurred and a belt surface ina joint part. In this case, in the second operation example, thecorrection processing period is stored in a storing unit serving asstoring means provided in a not-shown signal generating unit serving asspecific control signal output means. This signal generating unitoutputs a mark control signal (specific control signal) of an L levelduring the correction processing period stored in the storing unit andoutputs a mark control signal of an H level during other periods. Themark control signals are input to the microcomputer 4135.

Here, in the turned-up part of the linear scale 4108 adjacent on adownstream side in an endless moving direction of the boundary, a lightreceiving level is made unstable as shown in FIG. 91A and an outputpulse is also made unstable as shown in FIG. 91B. Thus, in the secondoperation example, the control using a dummy pulse is also applied to aperiod C of an unstable signal part present immediately before thisdiscontinuous part. Therefore, the correction processing period is setto start at start time of the period C of the unstable signal partpresent immediately before the discontinuous part and end at end time ofthe period A of the discontinuous part. However, since the turn-up atthe end of the linear scale 4108 occurs due to use over time, it is notpreferable to set a correction processing time from the beginning andstore the correction processing time in the storage unit of the signalgenerating unit. This is because, if the turn-up at the end occurs,since a width of a joint changes according to an amount of the turn-up,an appropriate correction processing period is not obtained even if acorrection processing period is set from the beginning assuming that ajoint is fixed.

Thus, in the second operation example, when it is judged in S4 that acount number is not within the defined range, that point is grasped as apoint when the boundary with the belt surface in the joint part passesthe detection area of the surface sensor 4109. Then, a correctionprocessing period, which has a point earlier than the point by timeequivalent to the period C of the unstable signal part as start time andthe end of the period A of the discontinuous part as end time, is storedin the storing unit of the signal generating unit (S12). Consequently,after turn-up at the end occurs, drive control taking into account anunstable signal part due to the turned-up part (drive control using adummy pulse) cannot be performed when the turned-up part passes thedetection area of the surface sensor 4109 for the first time, but thedrive control taking into account the unstable signal part can beperformed when the turned-up part passes the detection area of thesurface sensor 4109 after that.

Thereafter, when an amount of turn-up at the end of the linear scale isfurther increased, before a correction processing time set at that pointbegins (S11), a count number is not within the defined range (S4). Inthis case, a new correction processing period is stored in the storingunit of the signal generation unit.

As described above, in the second operation example, as shown in FIG.91C, a correction processing period is set to a period obtained byadding the period C immediately before a discontinuous part, in which anunstable signal part is present in an output pulse, immediately beforethe period A of the discontinuous part. Consequently, even if anunstable signal part is present in a part immediately before adiscontinuous part due to the turn-up at the end of the linear scale4108, the feedback control system can perform appropriate feedbackcontrol. The same holds true at the time when an unstable signal part ispresent in a part immediately before a discontinuous part due to othercauses.

Note that, in the second operation example, the period immediatelybefore the period A of the discontinues part is the period coincidingwith the period C in which an unstable signal part is present in anoutput pulse. However, the period may be a period longer than the periodC to secure a margin taking into account an error.

In the explanation of the second operation example, both start time andend time of a correction processing period are stored in the storingunit of the signal generating unit, and a mark control signal of an Llevel is output during this correction processing period. However, onlythe start time of the correction processing period may be stored in thestoring unit. In this case, the end time of the correction processingperiod only has to be a point when the count number returns to thedefined range in S4.

In addition, a correction processing period may be set from thebeginning assuming occurrence of turn-up at the end of the linear scale4108 to store the correction processing period in the storing unit ofthe signal generating unit. In this case, if the turn-up at the end hasoccurred more than assumed, a new correction processing period is storedin the storing unit of the signal generating unit as described above.

A third operation example will be explained. In the third operationexample, a stain due to a toner adheres on the linear scale 4108 asshown in FIG. 82 and appropriate drive control cannot be performedimmediately before and after a discontinuous part (this operationexample will be hereinafter referred to as “third operation example”).

When a stain due to a toner adheres on the linear scale 4108,immediately before and after a discontinuous part, a light receivinglevel is made unstable as indicated by a broken line in FIG. 93A, and anoutput pulse is also made unstable as shown in FIG. 93B. Note that FIG.93C shows a mark control signal (specific control signal), which is anoutput signal from the signal generating unit, as in the secondoperation example.

A basic flow of control in a feedback control system in the thirdoperation example is the same as that in the second operation example.The third operation example is different from the second operationexample only in a correction processing period to be stored in thestoring unit of the signal generating unit. In short, in the thirdoperation example, the correction processing period is set to start atstart time of a period D of an unstable signal part due to a spreadtoner present immediately before a discontinuous part and end at endtime of a period E of the unstable signal part due to a spread tonerpresent immediately after the discontinuous part. However, it isdifficult to grasp in advance where on the linear scale 4108 and towhich degree the stain due to a toner adheres. Therefore, it isimpossible to set a correction processing period from the beginning andstore the correction processing period in the storing unit of the signalgenerating unit.

Thus, in the third operation example, as in the case of the secondoperation example, when it is judged in S4 that a count number is notwithin a defined range, it is grasped that a stain part is present inthe detection area of the surface sensor 4109. Then, a correctionprocessing period, which has a point earlier than the grasped start time(start time of the discontinuous part) by time equivalent to the periodD of the unstable signal part as start time and a point advanced by timeequivalent to a period E of the unstable signal part from the graspedend time (end time of the discontinuous part) as end time, is stored inthe storing unit of the signal generating unit. Consequently, after astain adheres, drive control taking into account an unstable signal partpresent immediately before the discontinuous part corresponding to thestain part (drive control using a dummy pulse) cannot be performed whenthe stain part passes the detection area of the surface sensor 4109 forthe first time, but the drive control taking into account the unstablesignal part present immediately before the discontinuous part can beperformed after that.

Thereafter, when the stain further spreads, the period A of thediscontinuous part also becomes longer. Thus, it is desirable to updatethe correction processing period according to such a change of theperiod A of the discontinuous part.

Note that, in the third operation example, periods immediate before andafter the period A of the discontinuous part are periods coinciding withthe periods D and E in which an unstable signal part is present in anoutput pulse, respectively. However, because of the same reason asdescribed above, the periods may be shorter or longer than the periods Dand E.

Next, an example of generation of a mask control signal for determiningthe correction processing period in the third operation example will beexplained. Note that, although the third operation example will beexplained in the following explanation, the same holds true for thefirst operation example and the second operation example.

A light receiving level of the surface sensor 4109 before and after adiscontinuous part is as shown in FIGS. 93A and 94A. When a signal ofthis light receiving level is passed through a low pass filter servingas filtering means, a frequency component equivalent to time intervalsof signal parts corresponding to respective marks is removed, and a lowfrequency signal as indicated by an alternate long and short dash lineshown in FIG. 94A is obtained. Then, a signal level of this lowfrequency signal and a predetermined threshold level (threshold value) Sare compared to generate a mask control signal as shown in FIG. 94B.This mask control signal is at an H level if a signal level of the lowfrequency signal is equal to or higher than the predetermined thresholdlevel S and at an L level if the signal level is lower than thepredetermined threshold level S. It is possible to provide a mechanismfor generating such a mask control signal in the surface sensor 4109. Inthat case, the correction processing unit 4154 can perform simpleprocessing of judging whether this mask control signal is at the L levelinstead of the judgment in S4. In other words, the correction processingunit 4154 only has to perform simple processing of judging whether themask control signal input from the surface sensor 4109 is at the L levelrather than the processing for judging whether a count number is withina defined range as in S4.

Note that, in the explanations of the first to the third operationexample, a multiplied pulse obtained by multiplying an output pulse fromthe surface sensor 4109 to be sixty-four times as large in themultiplying unit 4152 is used as a feedback signal. However, the sameeffect can be obtained even if the output pulse is not multiplied andused as a feedback signal without providing such a multiplying unit4152.

In addition, in the explanations of the first to the third operationexample, it is judged whether a discontinuous part is present in anoutput pulse according to whether a pulse number counted everypredetermined sampling time is within the usual area a1. However, amethod of judging whether a discontinuous part is present in an outputpulse is not limited to this.

A differential signal shown in FIG. 95C is calculated from a referencepulse (reference signal) corresponding to target velocity shown in FIG.95A and an output pulse shown in FIG. 95B. This differential signalindicates how high or how low actual velocity of the rotating body suchas the belt 4106 or the drum 4126 is with respect to target velocity. Inother words, the differential signal indicates actual velocity of therotating body by taking into account the target velocity. A period, inwhich the actual velocity of the rotating body indicated by thedifferential signal is outside a defined range decided in advance, isjudged as a period of a discontinuous part. In the method of judging adiscontinuous part adopted in the first to the third operation examples,presence of a discontinuous part in an output pulse cannot be recognizedfrom the time when the discontinuous part starts to be present in theoutput pulse until the time when time equivalent to a pulse numberelapses. On the other, in the above-mentioned other methods, start timeand end time of a discontinuous part can be recognized only from onepulse immediately before start and immediate after end of thediscontinuous part in an output pulse and a corresponding referencepulse. Therefore, according to the other methods, the start time and theend time of the discontinuous part can be recognized earlier.Consequently, a time lag from the time when the discontinuous partappears in the output pulse until the time when the discontinuous partis recognized is reduced. As a result, drive control using a dummy pulsecan be preformed immediately after the discontinuous part starts to bepresent. Therefore, more stable drive control can be realized.

Note that, in the second operation example and the third operationexample, since the drive control using a dummy pulse is started fixedtime earlier than the time when the discontinuous part starts to bepresent, no useful effects is realized in particular even if the timelag is reduced during such drive control However, as described above, inthe second operation example and the third operation example, whenturn-up at the end or a stain part to be a discontinuous part passes thedetection area of the surface sensor 4109 for the first time, thefeedback control using a dummy pulse is performed from the time when itis judged that the discontinuous part is present as in the firstoperation example. Therefore, in the drive control at the time whenturn-up at the end or a stain part to be a discontinuous part passes thedetection area of the surface sensor 4109 for the first time, the effectof realizing stable drive control by reducing the time lag is useful.

As described above, the drive control device in the thirty-fifthembodiment detects the marks 4108 a, which are provided to continue atthe predetermined intervals over the endless moving direction of thebelt 4106 or the drum 4126 serving as a drive control object member,which moves endlessly, or the drive roller 4101, the driven roller 4104or 4105, or the driven pulley 4128 serving as an endless moving memberendlessly moving following the endless movement of the belt 4106 or thedrum 4126, with the surface sensor 4109 serving as mark detecting means.Then, the drive control device feedback-controls driving of the belt4106 or the drum 4126 using an output pulse that is a mark detectionsignal obtained by the detection. The drive control device also includesthe interface device for detection 4142 serving as feedback controlmeans, which performs feedback control using an alternative signalinstead of an output pulse for the discontinuous part A in an outputpulse in which intervals of signal parts corresponding to the respectivemarks are outside the range decided in advance (usual area a1) and atleast one of the signal parts B, C, D, and E immediately before and thesignal parts B, C, D, and E immediately after the discontinuous part,the microcomputer 4135, the instruction generating device 4139, and theinterface for motor drive 4140. With such a structure, as describedabove, even if the unstable signal parts B, C, D, and E are present inat least one of parts immediately before and immediately after thediscontinuous part A, the drive control device can perform theappropriate drive control using a dummy pulse.

In the thirty-fifth embodiment, the feedback control using a dummy pulseis applied to all of the unstable signal parts B, C, D, and E present inat least one of the parts immediately before and immediately after thediscontinuous part A. This makes it possible to prevent drive controlfrom being made unstable by the unstable signal parts.

In the first operation example of the thirty-fifth embodiment, the timerserving as specific control signal output means, which outputs a markcontrol signal serving as a specific control signal in a discontinuousperiod in which the discontinuous part is present in the output pulseand a fixed period decided in advance immediately after this period. Thedrive control device performs the feedback control using a dummy pulsewhile the mark control signal is output. This makes it possible toperform appropriate drive control without performing complicatedarithmetic processing even if the unstable signal part is presentimmediately after the discontinuous part.

In the second operation example of the thirty-fifth embodiment, thesignal generating unit serving as specific control signal output means,which outputs a mark control signal serving as a specific control signalin a discontinuous period in which the discontinuous part is present inthe output pulse and a fixed period decided in advance immediatelybefore this period. The drive control device performs the feedbackcontrol using a dummy pulse while the mark control signal is output.This makes it possible to perform appropriate drive control withoutperforming complicated arithmetic processing even if the unstable signalpart is present immediately before the discontinuous part.

In the third operation example of the thirty-fifth embodiment, thesignal generating unit serving as specific control signal output means,which outputs a mark control signal serving as a specific control signalin a discontinuous period in which the discontinuous part is present inthe output pulse, a fixed period decided in advance immediately afterthe discontinuous period, and a fixed period decided in advanceimmediately before the discontinuous period. The drive control deviceperforms the feedback control using a dummy pulse while the mark controlsignal is output. This makes it possible to perform appropriate drivecontrol without performing complicated arithmetic processing even if theunstable signal parts are present immediately before and immediatelyafter the discontinuous part.

In the second operation example and the third operation example of thethirty-fifth embodiment, the storing unit serving as storing means,which stores start time of the discontinuous part in the output pulse,is provided. An output of a mark control signal is started the fixedperiod before the start time stored in the storing unit when adiscontinuous part appears in an output pulse the next time or after thenext time. This makes it possible to perform the drive control using adummy pulse surely in a period in which a unstable signal part ispresent immediately before the discontinuous part.

As explained in the second operation example and the third operationexample of the thirty-fifth embodiment, the velocity detecting unit,which detects endless moving velocity of the belt 4106 or the drum 4126,the drive roller 4101, the driven roller 4104 or 4105, or the drivenpulley 4128, is provided. Drive control is performed according towhether the endless moving velocity detected by this velocity detectingunit is outside a defined range. Consequently, as described above, atime lag from the time when a discontinuous part appears in an outputpulse until the time when the discontinuous part is recognized isreduced, and more stable drive control can be realized.

In the thirty-fifth embodiment, start time and end time of thediscontinuous period are set at timing when a signal, which is obtainedby removing a frequency component equivalent to time intervals of signalparts corresponding to respective marks from the output pulse, changesacross the threshold level S that is a predetermined threshold value.Consequently, the start time and the end time of the discontinuousperiod can be grasped clearly.

In the thirty-fifth embodiment, it is judged whether the discontinuouspart is present according to whether the number of signal partscorresponding to marks in the output pulse obtained in predeterminedsampling time is smaller than a defined number. The fixed period is setto time equivalent to time integer times as large as the sampling time.As described above, this makes it possible not to provide a clockgenerating circuit and to realize cost reduction.

In the thirty-fifth embodiment, the drive control device has theinterface device for detection 4142 constituting the multiplying unit4152 serving as multiplying means that generates a multiplied signalobtained by multiplying the output pulse to predetermined times aslarge. The drive control device performs feedback control using themultiplied signal in periods other than a period in which the feedbackcontrol using a dummy pulse is performed. With such a structure, asdescribed above, even if the surface sensor 4109 is a surface sensorwith low resolution, there is an effect of improving dummy resolution.In addition, concerning a continuous part in an output pulse or amultiplied pulse, an error range of a position of the belt 4106 or thedrum 4126 with respect to a target position can be reduced. As a result,an amount of maximum deviation, which could occur immediately after theperiod B of the discontinuous part ends, can be reduced. Therefore,rapid velocity variation in the belt 4106 or the drum 4106, which couldoccur immediately after the period B of the discontinuous part ends, canbe controlled. In particular, the PLL circuit serving as a multiplyingcircuit, which compares phases of a feedbacked multiplied pulse and anoutput pulse before multiplication and generates a multiplied pulseusing a result of the phase comparison, is used. This makes it possibleto generate a multiplied pulse with an inexpensive structure.

A thirty-sixth embodiment of the invention will be explained withreference to FIG. 96.

This embodiment is an example of application of the invention to a colorcopying machine serving as an image forming apparatus. Reference numeral1010 denotes an apparatus body. The apparatus body 1010 includes aphotosensitive drum 1012 serving as an image bearing member in a partslightly to the right in an armor case 1011. Around the photosensitivedrum 1012, a rotating type developing device 1014 serving as developingmeans, an intermediate transfer unit 1015, a cleaning device 1016, acharge eliminating device 1017, and the like are arranged in order in arotating direction indicated by arrow (counterclockwise) from a chargingdevice 1014 set above the photosensitive drum 1012.

Above these charging device 1013, the rotating type developing device1014, the cleaning device 1016, and the charge eliminating device 1017,an optical writing device serving as exposing means, for example, alaser writing device 1018 is set. The rotating type developing device1014 includes developing devices 1020A, 1020B, 1020C, and 1020D havingdeveloping rollers 1021, in which toners of colors yellow, magenta,cyan, and black are contained, respectively. The rotating typedeveloping device 1014 rotates around an axis thereof to selectivelymove the developing devices 1020A, 1020B, 1020C, and 1020D of therespective colors to developing positions opposed to an outer peripheryof the photosensitive drum 1012.

In the intermediate transfer unit 1015, an endless intermediate transfermember serving as an image bearing member, for example, an intermediatetransfer belt 1024 is laid over plural rollers 1023. This intermediatetransfer belt 1024 is brought into abutment against the photosensitivedrum 1012. A transfer device 1025 is set on an inner side of theintermediate transfer belt 1024, and a transfer device 1026 and acleaning device 1027 are set on an outer side of the intermediatetransfer belt 1024. The cleaning device 1027 is provided to be capableof approaching and separating from the intermediate transfer belt 1024freely.

Image signals of the respective colors are input to the laser writingdevice 1018 from the image reading apparatus 1029 via a not-shown imageprocessing unit. The laser writing device 1018 irradiates laser beams L,which are sequentially modulated by the image signals of the respectivecolors, on the photosensitive drum 1012 in a uniformly charged state andexposes the photosensitive drum 1012 to light to thereby formelectrostatic latent images on the photosensitive drum 1012.

The image reading apparatus 1029 subjects an image of an original G seton an original stand 1030, which is provided on an upper surface of theapparatus body 1010, to color separation to read and convert the imageinto electric image signals. A recording medium conveying path 1032conveys a recording medium like a sheet from the right to the left. Inthe recording medium conveying path 1032, a registration roller pair1033 is set before the intermediate transfer unit 1015 and the transferdevice 1026, and a conveying belt 1034, a fixing device 1035, and asheet discharging roller pair 1036 are arranged further on a downstreamside than the intermediate transfer unit 1015 and the transfer device1026.

The apparatus body 1010 is mounted on a sheet feeding device 1050.Plural sheet feeding cassettes 1051 are provided in multiple stages inthe sheet feeding device 1050. One of sheet feeding rollers 1052 isselectively driven to deliver a recording medium from one of the sheetfeeding cassettes 1051. This recording medium is conveyed to therecording medium conveying path 1032 through an automatic sheet feedingpath 1037 in the apparatus body 1010.

A hand-supply tray 1038 is provided to be capable of opening and closingfreely on the right side of the apparatus body 1010. A recording mediuminserted from the hand-supply tray 1038 is conveyed to the recordingmedium conveying path 1032 through a hand-supply sheet feeding path 1039in the apparatus body 1010. A not-shown sheet discharge tray isdetachably attached on the left side of the apparatus body 1010. Arecording medium discharged by the sheet discharging roller pair 1036 ishoused in the sheet discharge tray through the recording mediumconveying path 1032.

In this color copying machine, when a user makes a color copy of anoriginal G, the user sets the original G on the original stand 1030 andpresses a not-shown start switch. Then, a copying operation is started.First, the image reading apparatus 1029 subjects an image of theoriginal G on the original stand 1030 to color separation to read theimage.

At the same time, a recording medium is selectively delivered by thesheet feeding roller 1052 from the sheet feeding cassette 1051 in thesheet feeding device 1050. This recording medium collides with theregistration roller pair 1033 through the recording medium conveyingpath 1032 and stops.

The photosensitive drum 1012 rotates counterclockwise, and theintermediate transfer belt 1024 rotates clockwise according to rotationof a drive roller of the rollers 1023. The photosensitive drum 1012 ischarged uniformly by the charging device 1013 according to the rotation.A laser beam modulated by an image signal of a first color, which isgiven to the laser writing device 1018 via the image processing unitfrom the image reading apparatus 1029, is irradiated on thephotosensitive drum 1012 from the laser writing device 1018 to form anelectrostatic latent image on the photosensitive drum 1012.

The electrostatic latent image on the photosensitive drum 1012 isdeveloped by a developing device 1020A of the first color of therotating type developing device 1014 to be changed to an image of thefirst color. The image of the first color on the photosensitive drum1012 is transferred onto the intermediate transfer belt 1024 by thetransfer device 1025. The photosensitive drum 1012 is cleaned by thecleaning device 1016 after the transfer of the image of the first colorto have a residual toner removed and is subjected to charge eliminationby the charge eliminating device 1017.

Subsequently, the photosensitive drum 1012 is uniformly charged by thecharging device 1013. A laser beam modulated by an image signal of asecond color, which is given to the laser writing device 1018 via theimage processing unit from the image reading apparatus 1029, isirradiated on the photosensitive drum 1012 from the laser writing device1018 to form an electrostatic latent image on the photosensitive drum1012. The electrostatic latent image on the photosensitive drum 1012 isdeveloped by a developing device 1020B of the second color of therotating type developing device 1014 to be changed to an image of thesecond color. The image of the second color on the photosensitive drum1012 is transferred onto the intermediate transfer belt 1024 by thetransfer device 1025 to be superimposed on the image of the first color.The photosensitive drum 1012 is cleaned by the cleaning device 1016after the transfer of the image of the second color to have a residualtoner removed and is subjected to charge elimination by the chargeeliminating device 1017.

Next, the photosensitive drum 1012 is uniformly charged by the chargingdevice 1013. A laser beam modulated by an image signal of a third color,which is given to the laser writing device 1018 via the image processingunit from the image reading apparatus 1029, is irradiated on thephotosensitive drum 1012 from the laser writing device 1018 to form anelectrostatic latent image on the photosensitive drum 1012. Theelectrostatic latent image on the photosensitive drum 1012 is developedby a developing device 1020C of the third color of the rotating typedeveloping device 1014 to be changed to an image of the third color. Theimage of the third color on the photosensitive drum 1012 is transferredonto the intermediate transfer belt 1024 by the transfer device 1025 tobe superimposed on the images of the first color and the second color.The photosensitive drum 1012 is cleaned by the cleaning device 1016after the transfer of the image of the third color to have a residualtoner removed and is subjected to charge elimination by the chargeeliminating device 1017.

Moreover, the photosensitive drum 1012 is uniformly charged by thecharging device 1013. A laser beam modulated by an image signal of afourth color, which is given to the laser writing device 1018 via theimage processing unit from the image reading apparatus 1029, isirradiated on the photosensitive drum 1012 from the laser writing device1018 to form an electrostatic latent image on the photosensitive drum1012. The electrostatic latent image on the photosensitive drum 1012 isdeveloped by a developing device 1020D of the fourth color of therotating type developing device 1014 to be changed to an image of thefourth color. The image of the fourth color on the photosensitive drum1012 is transferred onto the intermediate transfer belt 1024 by thetransfer device 1025 to be superimposed on the images of the firstcolor, the second color, and the third color to form a full color image.

The photosensitive drum 1012 is cleaned by the cleaning device 1016after the transfer of the image of the fourth color to have a residualtoner removed and is subjected to charge elimination by the chargeeliminating device 1017.

Then, the registration roller pair 1033 rotates in timing to deliver arecording medium. The full color image on the intermediate transfer belt1024 is transferred onto this recording medium by the transfer device1026. The full color image is conveyed by the conveying belt 1034 tohave the full color image fixed thereon by the fixing device 1035 and isdischarged to the sheet discharge tray by the sheet discharging rollerpair 1036. In addition, the intermediate transfer belt 1024 is cleanedby the cleaning device 1027 after the transfer of the full color imageto have a residual toner removed.

The above explanation is about an operation for forming four-colorimage. When a three-color image is formed, three single color images aresequentially formed on the photosensitive drum 1012, transferred ontothe intermediate transfer belt 1024 to be superimposed one on top ofanother, and then collectively transferred onto a recording medium. Whena two-color image is formed, two single color images are sequentiallyformed on the photosensitive drum 1012, transferred onto theintermediate transfer belt 1024 to be superimposed one on top of theother, and then collectively transferred onto a recording medium.

In such a color copying machine, driving accuracy of the photosensitivedrum 1012, the intermediate transfer belt 1024, and the conveying belt1034, which serve as image bearing members, significantly affects aquality of a final image. Thus, more highly accurate driving for thesemembers is desired.

Thus, in this embodiment, driving for the photosensitive drum 1012 isperformed by the drive apparatuses described in the first embodiment tothe thirty-fifth embodiment (e.g., the drive apparatus shown in FIG. 38)and driving for the intermediate transfer belt 1024 and the conveyingbelt 1034 is performed by the drive apparatuses described in the firstembodiment to the thirty-fifty embodiment (e.g., the drive apparatusshown in FIG. 39) based on the above-mentioned method of controlling aposition of a rotating body.

Therefore, accuracy of driving of the image bearing members is improved,and a high quality image can be obtained.

A thirty-seventh embodiment of the invention will be explained withreference to FIG. 97.

In a color copying machine serving as an image forming apparatus in thisembodiment, a photosensitive member 1060 serving as an image bearingmember is a photosensitive belt in which a photosensitive layer of anorganic photoconductor (OPC) or the like is formed in a thin film shapeon an outer peripheral surface of a belt base material of nickel (Ni)formed in a closed loop shape. This photosensitive member 1060 issupported by three photosensitive conveying rollers 1061 to 1063 androtated in a direction of arrow A by a drive motor (not shown).

Around the photosensitive member 1060, a charging device 1064, anexposure optical system (hereinafter referred to as LSU) 1065 serving asexposing means, developing devices 1066 to 1069 of colors black, yellow,magenta, and cyan, an intermediate transfer unit 1070, a photosensitivecleaning unit 1071, and a charge eliminating device 1072 are provided inorder in a rotating direction of the photosensitive member 1060indicated by arrow A.

A high voltage of about −4 to 5 kilovolts is applied to the chargingdevice 1064 from a not-shown power supply device. The charging device1064 charges a part of the photosensitive member 1060 opposed to thecharging device 1064 to give a uniform charging potential to the part.

The LSU 1065 sequentially subjects image signals of the respectivecolors from a gradation converting unit (not shown) to light intensitymodulation and pulse width modulation with a laser driving circuit (notshown) and drives a semiconductor laser (not shown) with a signal of themodulation to thereby obtain an exposure beam 1073. Then, the LSU 1065scans the photosensitive member 1060 with this exposure beam 1073 tosequentially form electrostatic latent images corresponding to the imagesignals of the respective colors on the photosensitive member 1060.

A joint sensor 1074 detects a joint of the photosensitive member 1060formed in a loop shape. When the joint sensor 1074 detects the joint ofthe photosensitive member 1060, the timing controller 1075 controlslight emitting timing of the LSU 1065 such that the joint of thephotosensitive member 1060 is avoided and positions, where theelectrostatic latent images of the respective colors are formed, aremade identical.

The respective developing devices 1066 to 1069 contain tonerscorresponding to respective developing colors. The developing devices1066 to 1069 come into abutment against the photosensitive member 1060selectively at timing according to electrostatic latent imagescorresponding to image signals of the respective colors on thephotosensitive member 1060, develop the electrostatic latent images onthe photosensitive member 1060 with the toners, and change theelectrostatic latent images to image of the respective colors to therebyform a full color image consisting of a four-color image.

The intermediate transfer unit 1070 includes a transfer drum 1076serving as an intermediate transfer member, which is obtained bywrapping a belt-like sheet made of conductive resin or the like around apipe of metal like aluminum, and an intermediate transfer membercleaning unit 1077 obtained by forming rubber or the like in a bladeshape. The intermediate transfer member cleaning unit 1077 is separatedfrom the intermediate transfer member 1076 while a four-color image isbeing formed on the intermediate transfer member 1076.

Only in cleaning the intermediate transfer member 1076, the intermediatetransfer member cleaning unit 1077 comes into abutment against theintermediate transfer member 1076 to remove a toner, which remainswithout being transferred onto recording paper 1078 serving as arecording medium, from the intermediate transfer member 1076. Therecording paper 1078 is delivered to a sheet conveying path 1081 one byone from a recording paper cassette 1079 by a sheet feeding roller 1080.

A transfer unit 1082 serving as transfer means transfers a full colorimage on the intermediate transfer member 1076 onto the recording paper1078. The transfer unit 1082 includes a transfer belt 1083 that isobtained by forming conductive rubber or the like in a belt shape, atransfer device 1084 that applies a transfer bias for transferring thefull color image on the intermediate transfer member 1076 onto therecording paper 1078 to the intermediate transfer member 1076, and aseparating device 1085 that applies a bias to the intermediate transfermember 1076 to prevent the recording paper 1078 from sticking to theintermediate transfer member 1076 electrostatically after the full colorimage is transferred onto the recording paper 1078.

The fixing device 1086 includes a heat roller 1087 having a heat sourcein the inside thereof and a pressure roller 1088. The fixing device 1086applies pressure and heat to the recording paper 1078 according torecording paper nipping rotation of the heat roller 1087 and thepressure roller 1088 and fixes the full color image on the recordingpaper 1078 to form a full color image.

An operation of the color copying machine constituted as described abovewill be hereinafter explained. In the explanation, it is assumed thatdevelopment of electrostatic latent images is performed in an order ofblack, cyan, magenta, and yellow.

The photosensitive member 1060 and the intermediate transfer member 1076are driven in directions of arrows A and B by drive sources (not show),respectively. In this state, first, a high voltage of about −4 to 5kilovolts is applied to the charging device 1064 from a power supplydevice (not shown), and the charging device 1064 charges the surface ofthe photosensitive member 1060 to about −700 volts uniformly.

Next, when the joint sensor 1074 detects the joint of the photosensitivemember 1060, the LSU 1065 irradiates the exposure beam 1073 of a laserbeam corresponding to an image signal of black on the photosensitivemember 1060 when fixed time elapses after the detection to avoid thejoint of the photosensitive member 1060. A charge in a part of thephotosensitive member 1060, on which the exposure beam 1073 isirradiated, is eliminated, and an electrostatic latent image is formedon the photosensitive member 1060.

On the other hand, the black developing device 1066 is brought intoabutment against the photosensitive member 1060 at predetermined timing.A negative charge is given to a black toner in the black developingdevice 1066 in advance. The black toner adheres to only a part of thephotosensitive member 1060 where a charge is eliminated by irradiationof the exposure beam 1073 (electrostatic latent image part), anddevelopment by a so-called negative positive process is performed.

The black toner image formed on the surface of the photosensitive member1060 by the black developing device 1066 is transferred onto theintermediate transfer member 1076. A residual toner, which has not beentransferred onto the intermediate transfer member 1076 from thephotosensitive member 1060, is removed by the photosensitive membercleaning unit 1071, and the charge on the photosensitive member 1060 iseliminated by the charge eliminating device 1072.

Next, the charging device 1064 charges the surface of the photosensitivemember 1060 to about −700 volts uniformly. Then, when the joint sensor1074 detects the joint of the photosensitive member 1060, the LSU 1065irradiates the exposure beam 1073 of a laser beam corresponding to animage signal of cyan on the photosensitive member 1060 when fixed timeelapses after the detection to avoid the joint of the photosensitivemember 1060. A charge in a part of the photosensitive member 1060, onwhich the exposure beam 1073 is irradiated, is eliminated, and anelectrostatic latent image is formed on the photosensitive member 1060.

On the other hand, the cyan developing device 1067 is brought intoabutment against the photosensitive member 1060 at predetermined timing.A negative charge is given to a cyan toner in the cyan developing device1067 in advance. The cyan toner adheres to only a part of thephotosensitive member 1060 where a charge is eliminated by irradiationof the exposure beam 1073 (electrostatic latent image part), anddevelopment by the so-called negative positive process is performed.

The cyan toner image formed on the surface of the photosensitive member1060 by the cyan developing device 1067 is transferred onto theintermediate transfer member 1076 to be superimposed on the black tonerimage. A residual toner, which has not been transferred onto theintermediate transfer member 1076 from the photosensitive member 1060,is removed by the photosensitive member cleaning unit 1071, and thecharge on the photosensitive member 1060 is removed by the chargeeliminating device 1072.

Next, the charging device 1064 charges the surface of the photosensitivemember 1060 to about −700 volts uniformly. Then, when the joint sensor1074 detects the joint of the photosensitive member 1060, the LSU 1065irradiates the exposure beam 1073 of a laser beam corresponding to animage signal of magenta on the photosensitive member 1060 when fixedtime elapses after the detection to avoid the joint of thephotosensitive member 1060. A charge in a part of the photosensitivemember 1060, on which the exposure beam 1073 is irradiated, iseliminated, and an electrostatic latent image is formed on thephotosensitive member 1060.

On the other hand, the magenta developing device 1068 is brought intoabutment against the photosensitive member 1060 at predetermined timing.A negative charge is given to a magenta toner in the magenta developingdevice 1068 in advance. The magenta toner adheres to only a part of thephotosensitive member 1060 where a charge is eliminated by irradiationof the exposure beam 1073 (electrostatic latent image part), anddevelopment by the so-called negative positive process is performed.

The magenta toner image formed on the surface of the photosensitivemember 1060 by the magenta developing device 1068 is transferred ontothe intermediate transfer member 1076 to be superimposed on the blacktoner image and the cyan toner image. A residual toner, which has notbeen transferred onto the intermediate transfer member 1076 from thephotosensitive member 1060, is removed by the photosensitive membercleaning unit 1071, and the charge on the photosensitive member 1060 iseliminated by the charge eliminating device 1072.

Moreover, the charging device 1064 charges the surface of thephotosensitive member 1060 to about −700 volts uniformly. Then, when thejoint sensor 1074 detects the joint of the photosensitive member 1060,the LSU 1065 irradiates the exposure beam 1073 of a laser beamcorresponding to an image signal of yellow on the photosensitive member1060 when fixed time elapses after the detection to avoid the joint ofthe photosensitive member 1060. A charge in a part of the photosensitivemember 1060, on which the exposure beam 1073 is irradiated, iseliminated, and an electrostatic latent image is formed on thephotosensitive member 1060.

On the other hand, the yellow developing device 1069 is brought intoabutment against the photosensitive member 1060 at predetermined timing.A negative charge is given to a yellow toner in the yellow developingdevice 1069 in advance. The yellow toner adheres to only a part of thephotosensitive member 1060 where a charge is eliminated by irradiationof the exposure beam 1073 (electrostatic latent image part), anddevelopment by the so-called negative positive process is performed.

The yellow toner image formed on the surface of the photosensitivemember 1060 by the yellow developing device 1069 is transferred onto theintermediate transfer member 1076 to be superimposed on the black tonerimage, the cyan toner image, and the magenta toner image, and a fullcolor image is formed on the intermediate transfer member 1076. Aresidual toner, which has not been transferred onto the intermediatetransfer member 1076 from the photosensitive member 1060, is removed bythe photosensitive member cleaning unit 1071, and the charge on thephotosensitive member 1060 is eliminated by the charge eliminatingdevice 1072.

The transfer belt 1083, which has been separated from the intermediatetransfer member 1076, comes into contact with the intermediate transfermember 1076, and a high voltage of about +1 kilovolt is applied to thetransfer device 1084 from the power supply device (not shown), wherebythe full color image formed on the intermediate transfer member 1076 iscollectively transferred onto the recording paper 1078, which isconveyed along the sheet conveying path 1081 from the recording papercassette 1079, by the transfer device 1084.

A voltage is applied to the separating device 1085 from the power supplydevice such that an electrostatic force for attracting the recordingpaper 1078 acts, and the recording paper 1078 is separated from theintermediate transfer member 1076. Subsequently the recording paper 1078is sent to the fixing device 1086. In the fixing device 1086, the fullcolor image is fixed on the recording paper 1078 by a nipping pressureof the heat roller 1087 and the pressure roller 1088 and heat of theheat roller 1088. The recording paper 1078 is discharged to thedischarge tray 1090 by the sheet discharging roller pair 1089.

A residual toner on the intermediate transfer member 1076, which has notbeen transferred onto the recording paper 1078 by the transfer unit1082, is removed by the intermediate transfer member cleaning unit 1077.The intermediate transfer member cleaning unit 1077 is in a positionseparated from the intermediate transfer member 1076 until the fullcolor image is obtained. After the full color image is transferred ontothe recording paper 1078, the intermediate transfer member cleaning unit1077 comes into contact with the intermediate transfer member 1076 toremove the residual toner on the intermediate transfer member 1076. Theformation of a full color image for one sheet ends according to theseries of operations.

In such a color copying machine, driving accuracy of the photosensitivebelt 1060, the transfer drum 1076, and the transfer belt 1083significantly affects a quality of a final image. In particular, morehighly accurate driving for the photosensitive belt 106 and the transferbelt 1083 is desired.

Thus, in this embodiment, driving for the photosensitive belt 1060 andthe transfer belt 1083 is performed by the drive apparatuses describedin the first embodiment to the thirty-fifth embodiment (e.g., the driveapparatus shown in FIG. 38) and driving for the transfer drum 1076 isperformed by the drive apparatuses described in the first embodiment tothe thirty-fifty embodiment (e.g., the drive apparatus shown in FIG. 39)based on the above-mentioned method of controlling a position of arotating body.

Therefore, accuracy of driving of the image bearing members is improved,highly accurate sheet conveying drive can be performed, and a highquality image can be obtained.

A thirty-eighth embodiment of the invention will be explained withreference to FIG. 98.

This embodiment describes an example of application of the invention toan image forming apparatus of a tandem system. In this embodiment,plural image forming units 221Bk, 221M, 221Y, and 221C, which formimages of plural colors, for example, black (hereinafter referred to asBk), magenta (hereinafter referred to as M), yellow (hereinafterreferred to as Y), and cyan (hereinafter referred to as C),respectively, are arranged in the vertical direction. The image formingunits 221Bk, 221M, 221Y, and 221C include image bearing members 222Bk,222M, 222Y, and 222C consisting of a photosensitive member of a drumshape, respectively, charging devices (e.g., contact charging devices)223Bk, 223M, 223Y, and 223C, developing devices 224Bk, 224M, 224Y, and224C, cleaning devices 225Bk, 225M, 225Y, and 225C, and the like.

The photosensitive members 222Bk, 222M, 222Y, and 222C are arranged inthe vertical direction to be opposed to an endless direct transfer belt(conveying transfer belt) 226 and are driven to rotate at the sameperipheral velocity as the direct transfer belt 226. The photosensitivemembers 222Bk, 222M, 222Y, and 222C are uniformly charged by thecharging devices 223Bk, 223M, 223Y, and 223C, respectively, and thenexposed to light by exposing units 227Bk, 227M, 227Y, and 227Cconsisting of optical writing devices, whereby electrostatic latentimages are formed thereon.

The optical writing devices 227Bk, 227M, 227Y, and 227C drive asemiconductor laser with a semiconductor laser drive circuit accordingto image signals of the respective colors Y, M, C, and Bk and deflectlaser beams from the semiconductor laser with polygon mirrors 229Bk,229M, 229Y, and 229C to use the laser beams for scanning. Then, theoptical writing devices 227Bk, 227M, 227Y, and 227C focus the respectivelaser beams from the polygon mirrors 229Bk, 229M, 229Y, and 229C on thephotosensitive members 222Bk, 222M, 222Y, and 222C via not-shown fθlenses and mirrors to thereby expose the photosensitive members 222Bk,222M, 222Y, and 222C to light to form electrostatic latent images.

The electrostatic latent images on the photosensitive members 222Bk,222M, 222Y, and 222C are developed by the developing devices 224Bk,224M, 224Y, and 224C, respectively, to be changed to toner images of therespective colors Bk, M, Y, and C. Therefore, the charging devices223Bk, 223M, 223Y, and 223C, the optical writing devices 227Bk, 227M,227Y, and 227C, and the developing devices 224Bk, 224M, 224Y, and 224Cconstitute an image forming unit that forms images (toner images) of therespective colors Bk, M, Y, and C on the photosensitive members 222Bk,222M, 222Y, and 222C.

On the other hand, transfer paper like plain paper or an OHP sheet isfed to a registration roller 10231 along a transfer paper conveying pathfrom a sheet feeding device 230, which is constituted by using sheetfeed cassettes, set in a lower part of the image forming apparatus inthis embodiment. The registration roller 10231 delivers the transferpaper to a transfer nip portion of the direct transfer belt 226 and thephotosensitive member 222Bk in timing with the toner image on thephotosensitive member 222Bk in the image forming unit of a first color(image forming unit that transfers an image on a photosensitive memberto transfer paper first) 221Bk.

The direct transfer belt 226 is laid over a drive roller 10232 and adriven roller 10233 arranged in the vertical direction. The drive roller10232 is driven to rotate by a not-shown drive unit, and the directtransfer belt 226 rotates at the same peripheral velocity as thephotosensitive members 222Bk, 222M, 222Y, and 222C. The transfer paperdelivered from the registration roller 10231 is conveyed by the directtransfer belt 226. The toner images of the respective colors Bk, M, Y,and C on the photosensitive members 222Bk, 222M, 222Y, and 222C aresequentially transferred onto the transfer paper by an action of anelectric field formed by transfer units 234Bk, 234M, 234Y, and 234Cconsisting of corona chargers. Consequently, a full color image isformed on the transfer paper and, at the same time, the transfer paperis electrostatically attracted by the direct transfer belt 226 andconveyed surely.

The transfer paper is subjected to charge elimination by a separatingunit 236 consisting of a separating charger and separated from thedirect transfer belt 226. Then, the full color image is fixed on thetransfer paper by the fixing device 237, and the transfer paper isdischarged to a sheet discharging unit 239 provided in an upper part ofthe image forming apparatus in this embodiment. In addition, thephotosensitive members 222Bk, 222M, 222Y, and 222C are cleaned by thecleaning devices 225Bk, 225M, 225Y, and 225C after the transfer of thetoner images and prepare for the next image forming operation.

In such a color copying machine, driving accuracy of the direct transferbelt 226 significantly affects a quality of a final image. Therefore,more highly accurate driving for the direct transfer belt 226 isdesired.

Thus, in this embodiment, driving for the direct transfer belt 226 isperformed by the drive apparatuses described in the first embodiment tothe thirty-fifth embodiment (e.g., the drive apparatus shown in FIG. 38)based on the above-mentioned method of controlling a position of arotating body.

Therefore, accuracy of driving of the image bearing members is improved,highly accurate sheet conveying drive can be performed, and a highquality image can be obtained.

A thirty-ninth embodiment of the invention will be explained withreference to FIG. 99.

This embodiment describes an example of application of the invention toa traveling body drive device of an image reading apparatus. In an imagereading apparatus shown in FIG. 96, reference numeral 901 denotes anoriginal to be read; 902, an original stand on which the original 901 ismounted; 903, an original lighting system that irradiates light on theoriginal 901; 904, an optical axis of reflected light; 905, an elementfor reading, for example, a charge coupled device (CCD); 906, a focusinglens; and 907, a total reflection mirror.

Reference numeral 908 denotes a photoelectric conversion unit consistingof the CCD 905, the lens 906, the mirror 907, and the like; 909 and 910,pulleys for sub-scanning drive; 911, a wire; 300, a driving motor; and912, a housing for an image scanner. In the photoelectric conversionunit 908 for reading an original, the driving motor 300 is fixed to thehousing 912 to drive the photoelectric conversion unit 908 in asub-scanning direction of the original 901 using means for transmittinga driving force of the motor such as the wire 911 and the pulleys 909and 910.

In this case, the lighting system for reading 903 like a fluorescenttube lights the original 901 on the original stand 902, and pluralmirrors 7 return a reflected light beam (an optical axis there of isdenoted by 904) to focus an image of the original 901 in a lightreceiving unit of an image sensor such as the CCD 905. Then, thephotoelectric conversion unit 908 scans the entire surface of theoriginal 901 to read the entire original.

A sensor 913, which indicates a reading start position, is set below theend of the original 901. The photoelectric conversion unit 908 isdesigned to rise between a home position HP and a reading start positionN to come into a steady state of uniform velocity and start readingafter reaching the HP point.

In this embodiment, driving for the photoelectric conversion unit 908 isperformed by the drive apparatuses described in the first embodiment tothe thirty-fifth embodiment (e.g., the drive apparatus shown in FIG. 38)based on the above-mentioned method of controlling a position of arotating body.

Therefore, accuracy of driving for the image reading apparatus isimproved, highly accurate sheet conveying drive can be performed, and ahigh quality image can be obtained.

A fortieth embodiment of the invention will be explained with referenceto FIG. 100.

FIG. 100 shows a personal computer that is an example of a computer usedfor executing the method of controlling a position of a rotating body.

Program for causing a personal computer 1001 to execute controloperations are stored in a CD-ROM 1003 serving as a recording medium.The personal computer 1001 can execute the control method by executingthe programs stored in the CD-ROM 1003.

As such programs, specifically, there are a control program for drivingto rotate a rotating body with a computer, a control program forcontrolling a photosensitive drum drive device of an image formingapparatus with a computer, a control program for controlling a transferdrum drive device of an image forming apparatus with a computer, acontrol program for controlling a traveling body drive device of animage reading apparatus with a computer, and the like. In FIG. 100,reference numeral 1002 denotes a disk drive, and 1004 denotes akeyboard.

As shown in FIG. 101, an IC card 165 serving as a recording medium maybe connected to a computer 106 serving as the control means to executethe programs for the method of controlling a position of a rotatingbody.

The computer 160 has an I/O interface 161, a CPU 162, a ROM 163, and aRAM 164. Programs for controlling a position of a rotating body forexecuting the method of controlling a position of a rotating bodyexplained in the embodiments are recorded in the IC card 165.

When the IC card 165 is connected, the CPU 162 of the computer 160accesses the IC card 165, reads the programs for controlling a positionof a rotating body stored in the IC card 165, and executes any one ofthe programs for controlling a position of a rotating body as required.

It is also possible to rewrite the programs stored in the ROM 163 withthe programs read from the IC card 165. In this case, the ROM 163 isconstituted by an electrically erasable/rewritable element like a flashmemory.

It is also possible to prepare a ROM in which the programs as describedabove are recorded and replace the already mounted ROM 163 with the ROM.

A forty-first embodiment of the invention will be explained withreference to FIG. 102.

In this embodiment, the computer 160 actuating an apparatus is connectedto a communication network via a network interface card (NIC) 166. TheCPU 162 accesses a server 167 on a side supplying a program forcontrolling a position of a rotating body, downloads the program forcontrolling a position for a rotating body recorded in a hard disk orthe like in the server 167, and rewrites a program stored in the ROM163. Consequently, it is possible to give the above-mentioned functionfor controlling a position of a rotating body to an existing imageforming apparatus easily.

A forty-second embodiment of the invention will be explained withreference to FIG. 103.

This embodiment is characterized in that a user is notified of failureor failure in the past of a unit 109 that reads a signal like a scalepulse (the surface sensor 2109 in FIG. 14, the surface sensor 3109 inFIG. 38, etc.) in the image forming apparatus or the image readingapparatus described above.

A user (operator) uses a not-shown apparatus body for outputting orreading an image. At this point, the user checks whether an output fromthe surface sensor 109, which always reads a scale (2108 in FIG. 14,3108 in FIG. 38, etc.) on a belt or a drum, is abnormal. In theapparatus body, a signal output unit 184 outputs a signal representing astate of the surface sensor 109.

A control unit 183 serving as an abnormality detecting unit (equivalentto the microcomputer 135 and the computer 160) receives a signal fromthe signal output unit 184. The control unit 183 judges a state of thesurface sensor 109 from information on whether an abnormal signal isreceived or a signal is not received normally. When abnormality hasoccurred, the control unit 183 informs an operation panel 185 serving asa display device (error display device) of the occurrence ofabnormality. When the operation panel 185 is informed of the occurrenceof abnormality, the operation panel 185 indicates the occurrence ofabnormality on a liquid crystal display unit 186 serving as a display.

Even when abnormality has occurred in the surface sensor 109 but thesurface sensor 109 has revived because of some situation, the operationpanel 185 indicates the occurrence of abnormality in the past on theliquid crystal display unit 186, whereby it is possible to inform a userof the occurrence of abnormality in the past. Consequently, the user canrecognize that a situation unmeasurable by the surface sensor 109 couldoccur and, when the surface sensor 109 actually breaks down, can copewith the failure calmly and accurately.

In this case, indication of occurrence of abnormality at present andindication of occurrence of abnormality in the past may be performed bydifferent methods. Other than indicting occurrence of abnormality on theliquid crystal display unit 186, the occurrence of abnormality may benotified to the user using voice or the like.

Moreover, a signal for exclusive use by a maintenance personnel may beused without notifying the user of occurrence of abnormality oroccurrence of abnormality in the past in the surface sensor 109. In thecase of the signal for exclusive use by a maintenance personnel, forexample, a display may be provided inside the apparatus body withoutindicating the occurrence of abnormality on the liquid crystal displayunit 186. Alternatively, when the apparatus is connected to a network,the occurrence of abnormality may be sent to a management section, whichperforms maintenance, through the network.

In the respective embodiments, control signals are two kinds of signals,namely, a first signal obtained from a belt or a drum itself and asecond signal obtained from a motor shaft or a shaft following the motorshaft, or a shaft supporting the belt (including a drive shaft).However, control signals may be three or more kinds of signals.

The embodiments of the invention have been explained. However, theinvention is not limited to the embodiments, and various alterations arepossible within a range not departing from the gist of the invention.

The invention can also be applied to a drive device for a photosensitivedrum, a transfer drum, a photosensitive belt, an intermediate transferbelt, or a sheet conveying belt, an image reading apparatus, a machinetool, a measurement apparatus, and the like.

Although the invention has been described with respect to a specificembodiment for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

1. A drive control device, comprising: a mark detecting unit thatdetects plural marks that are provided on a drive control object memberat a predetermined interval along a direction of movement of the drivecontrol object member, or that detects plural marks that are provided onan endless moving member at a predetermined interval along a directionof movement of the endless moving member, wherein the drive controlobject member and the endless moving member move endlessly, wherein themark detecting unit outputs a mark detection signal when a mark isdetected; and a feedback control unit that performs feedback controlusing an alternative signal instead of the mark detection signal atleast for a discontinuous part in the mark detection signal whereintervals of signal parts corresponding to the respective marks areoutside a range decided in advance, and the alternative signal is usedinstead of signal parts of the mark detection signal immediately beforeand after the discontinuous part.
 2. The drive control device accordingto claim 1, wherein the feedback control using the alternative signal isset such that all unstable signal parts of the mark detection signal arenot used by the feedback control unit.
 3. The drive control deviceaccording to claim 1, further comprising a specific control signaloutput unit that outputs a specific control signal in a discontinuousperiod, in which the discontinuous part is present in the mark detectionsignal, and a fixed period decided in advance immediately after thediscontinuous period, wherein the feedback control unit performs thefeedback control using the alternative signal while the specific controlsignal is output.
 4. The drive control device according to claim 3,wherein whether the discontinuous part is present depends on whether anumber of signal parts corresponding to marks in the mark detectionsignal obtained within a predetermined sampling time is smaller than adefined number, and the fixed period is set to a time that is integertimes as long as the sampling time.
 5. The drive control deviceaccording to claim 3, further comprising a velocity detecting unit thatdetects an endless moving velocity of the drive control object member orthe endless moving member, wherein whether the discontinuous part ispresent depends on whether the endless moving velocity detected by thevelocity detecting unit is outside a defined range.
 6. The drive controldevice according to claim 1, further comprising a specific controlsignal output unit that outputs a specific control signal in adiscontinuous period, in which the discontinuous part is present in themark detection signal, and a fixed period decided in advance immediatelybefore the discontinuous period, wherein the feedback control unitperforms the feedback control using the alternative signal while thespecific control signal is output.
 7. The drive control device accordingto claim 6, further comprising a storing unit that stores a start timeof the discontinuous part in the mark detection signal, wherein thespecific control signal output unit starts output of the specificcontrol signal the fixed period immediately before the discontinuouspart appears in the mark detection signal a next time or after the nexttime such that the specific control signal is output before the starttime of the discontinuous part stored in the storing unit.
 8. The drivecontrol device according to claim 1, further comprising a specificcontrol signal output unit that outputs a specific control signal in adiscontinuous period, in which the discontinuous part is present in themark detection signal, a fixed period decided in advance immediatelyafter the discontinuous period, and a fixed period decided in advanceimmediately before the discontinuous period, wherein the feedbackcontrol unit performs the feedback control using the alternative signalwhile the specific control signal is output.
 9. A drive control devicecomprising: a mark detecting unit that detects plural marks that areprovided on a drive control object member at a predetermined intervalalong a direction of movement of the drive control object member, orthat detects plural marks that are provided on an endless moving memberat a predetermined interval along a direction of movement of the endlessmoving member, wherein the drive control object member and the endlessmoving member move endlessly, wherein the mark detecting unit outputs amark detection signal when a mark is detected; a feedback control unitthat performs feedback control using an alternative signal instead ofthe mark detection signal at least for a discontinuous part in the markdetection signal where intervals of signal parts corresponding to therespective marks are outside a range decided in advance, and thealternative signal is used instead of signal parts of the mark detectionsignal immediately before and after the discontinuous part; and aspecific control signal output unit that outputs a specific controlsignal in a discontinuous period, in which the discontinuous part ispresent in the mark detection signal, and a fixed period decided inadvance immediately after the discontinuous period, wherein the feedbackcontrol unit performs the feedback control using the alternative signalwhile the specific control signal is output, and a start time and an endtime of the discontinuous period are set to a timing at which a signal,which is obtained by removing a frequency component equivalent to timeintervals of signal parts corresponding to the respective mark from themark detection signal, changes across a predetermined threshold value.10. A drive control device comprising; a mark detecting unit thatdetects plural marks that are provided on a drive control object memberat a predetermined interval along a direction of movement of the drivecontrol object member, or that detects plural marks that are provided onan endless moving member at a predetermined interval along a directionof movement of the endless moving member, wherein the drive controlobject member and the endless moving member move endlessly, wherein themark detecting unit outputs a mark detection signal when a mark isdetected; a feedback control unit that performs feedback control usingan alternative signal instead of the mark detection signal at least fora discontinuous part in the mark detection signal where intervals ofsignal parts corresponding to the respective marks are outside a rangedecided in advance, and the alternative signal is used instead of signalparts of the mark detection signal immediately before and after thediscontinuous part; and a multiplying unit that generates a multipliedsignal obtained by multiplying the mark detection signal to bepredetermined times as large, wherein the feedback control unit performsthe feedback control using the multiplied signal in periods other than aperiod in which the feedback control unit performs the feedback controlusing the alternative signal.
 11. The drive control device according toclaim 10, wherein a multiplying circuit, which compares phases of thefeedbacked multiplied signal and the mark detection signal beforemultiplication and generates a multiplied signal using a result of thephase comparison, is used as the multiplying unit.
 12. An image formingapparatus, comprising: a drive control object member that movesendlessly; and a drive control device that drive controls the drivecontrol object member, wherein the drive control device includes a markdetecting unit that detects plural marks that are provided on a drivecontrol object member at a predetermined interval along a direction ofmovement of the drive control object member, or that detects pluralmarks that are provided on an endless moving member at a predeterminedinterval along a direction of movement of the endless moving member,wherein the drive control object member and the endless moving membermove endlessly, wherein the mark detecting unit outputs a mark detectionsignal when a mark is detected; and a feedback control unit thatperforms feedback control using an alternative signal instead of themark detection signal at least for a discontinuous part in the markdetection signal where intervals of signal parts corresponding to therespective marks are outside a range decided in advance, and thealternative signal is used instead of signal parts of the mark detectionsignal immediately before and after the discontinuous part.
 13. An imagereading apparatus, comprising: a traveling body that irradiates light onan original surface or receives reflected light of light irradiated onthe original surface; a drive control object member, which movesendlessly, provided on a drive force transmission path for transmittinga drive force for causing the traveling body to travel along theoriginal surface; and a drive control device that drive controls thedrive control object member, wherein the drive control device includes amark detecting unit that detects plural marks that are provided on adrive control object member at a predetermined interval along adirection of movement of the drive control object member, or thatdetects plural marks that are provided on an endless moving member at apredetermined interval along a direction of movement of the endlessmoving member, wherein the drive control object member and the endlessmoving member move endlessly, wherein the mark detecting unit outputs amark detection signal when a mark is detected; and a feedback controlunit that performs feedback control using an alternative signal insteadof the mark detection signal at least for a discontinuous part in themark detection signal where intervals of signal parts corresponding tothe respective marks are outside a range decided in advance, and thealternative signal is used instead of signal parts of the mark detectionsignal immediately before and after the discontinuous part.